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devel / comp.arch.embedded / Re: Boxed MCU with RS-232 Port

SubjectAuthor
* Boxed MCU with RS-232 PortRick C
+* Re: Boxed MCU with RS-232 PortPaul Rubin
|`* Re: Boxed MCU with RS-232 PortRick C
| +* Re: Boxed MCU with RS-232 PortPaul Rubin
| |`* Re: Boxed MCU with RS-232 PortRick C
| | `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |  `* Re: Boxed MCU with RS-232 PortRick C
| |   +* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |`* Re: Boxed MCU with RS-232 PortRick C
| |   | `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |  `* Re: Boxed MCU with RS-232 PortRick C
| |   |   `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |    `* Re: Boxed MCU with RS-232 PortRick C
| |   |     `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |      `* Re: Boxed MCU with RS-232 PortRick C
| |   |       `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |        `* Re: Boxed MCU with RS-232 PortRick C
| |   |         `* Re: Boxed MCU with RS-232 PortPaul Rubin
| |   |          `* Re: Boxed MCU with RS-232 PortRick C
| |   |           `- Re: Boxed MCU with RS-232 PortPaul Rubin
| |   `* Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |    `* Re: Boxed MCU with RS-232 PortRick C
| |     `* Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |      +- Re: Boxed MCU with RS-232 PortAndrew Smallshaw
| |      `- Re: Boxed MCU with RS-232 PortRick C
| `- Re: Boxed MCU with RS-232 PortDavid Brown
+* Re: Boxed MCU with RS-232 PortTheo
|`* Re: Boxed MCU with RS-232 PortPaul Rubin
| `* Re: Boxed MCU with RS-232 PortTheo
|  +* Re: Boxed MCU with RS-232 PortDon Y
|  |`* Re: Boxed MCU with RS-232 PortRick C
|  | `* Re: Boxed MCU with RS-232 PortPaul Rubin
|  |  `* Re: Boxed MCU with RS-232 PortRick C
|  |   `- Re: Boxed MCU with RS-232 PortPaul Rubin
|  +* Re: Boxed MCU with RS-232 PortGrant Edwards
|  |+- Re: Boxed MCU with RS-232 PortRick C
|  |`- Re: Boxed MCU with RS-232 PortDon Y
|  `* Re: Boxed MCU with RS-232 PortRick C
|   +* Re: Boxed MCU with RS-232 PortTheo
|   |+- Re: Boxed MCU with RS-232 PortRick C
|   |`* Re: Boxed MCU with RS-232 PortPaul Rubin
|   | +* Re: Boxed MCU with RS-232 PortDon Y
|   | |`- Re: Boxed MCU with RS-232 PortDon Y
|   | `- Re: Boxed MCU with RS-232 PortTheo
|   `* Re: Boxed MCU with RS-232 PortHerbert Kleebauer
|    `* Re: Boxed MCU with RS-232 PortRick C
|     `* Re: Boxed MCU with RS-232 PortDimiter_Popoff
|      `* Re: Boxed MCU with RS-232 PortRick C
|       +- Re: Boxed MCU with RS-232 PortDimiter_Popoff
|       `* Re: Boxed MCU with RS-232 Portantispam
|        `* Re: Boxed MCU with RS-232 PortRick C
|         `* Re: Boxed MCU with RS-232 Portantispam
|          `* Re: Boxed MCU with RS-232 PortRick C
|           `* Re: Boxed MCU with RS-232 PortRick C
|            `* Re: Boxed MCU with RS-232 PortRick C
|             `* Re: Boxed MCU with RS-232 PortDimiter_Popoff
|              `- Re: Boxed MCU with RS-232 PortDon Y
+* Re: Boxed MCU with RS-232 Portpozz
|`- Re: Boxed MCU with RS-232 PortRick C
+* Re: Boxed MCU with RS-232 PortRick C
|+* Re: Boxed MCU with RS-232 PortPaul Rubin
||`* Re: Boxed MCU with RS-232 PortRick C
|| +* Re: Boxed MCU with RS-232 PortRick C
|| |+* Re: Boxed MCU with RS-232 PortTheo
|| ||`- Re: Boxed MCU with RS-232 PortRick C
|| |`* Re: Boxed MCU with RS-232 PortPaul Rubin
|| | `- Re: Boxed MCU with RS-232 PortRick C
|| `* Re: Boxed MCU with RS-232 PortPaul Rubin
||  `* Re: Boxed MCU with RS-232 PortRick C
||   +- Re: Boxed MCU with RS-232 PortPaul Rubin
||   `* Re: Boxed MCU with RS-232 PortHans-Bernhard Bröker
||    +* Re: Boxed MCU with RS-232 PortTheo
||    |+* Re: Boxed MCU with RS-232 PortRick C
||    ||+- Re: Boxed MCU with RS-232 PortTheo
||    ||+* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||`* Re: Boxed MCU with RS-232 PortRick C
||    ||| `* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||  +- Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||  `* Re: Boxed MCU with RS-232 PortRick C
||    |||   `* Re: Boxed MCU with RS-232 PortPaul Rubin
||    |||    `* Re: Boxed MCU with RS-232 PortRick C
||    |||     `- Re: Boxed MCU with RS-232 PortPaul Rubin
||    ||`* Re: Boxed MCU with RS-232 PortDon Y
||    || `* Re: Boxed MCU with RS-232 PortRick C
||    ||  +- Re: Boxed MCU with RS-232 PortDon Y
||    ||  `* Re: Boxed MCU with RS-232 PortGeorge Neuner
||    ||   +* Re: Boxed MCU with RS-232 PortRick C
||    ||   |+* Re: Boxed MCU with RS-232 PortJim Jackson
||    ||   ||+* Re: Boxed MCU with RS-232 PortDon Y
||    ||   |||+* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||`* Re: Boxed MCU with RS-232 PortDon Y
||    ||   |||| `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  +* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |`* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  | `* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |  `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  |   `* Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |    +* Re: Boxed MCU with RS-232 PortJim Jackson
||    ||   ||||  |    |+- Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  |    |`- Re: Boxed MCU with RS-232 PortDon Y
||    ||   ||||  |    `* Re: Boxed MCU with RS-232 PortRick C
||    ||   ||||  `* Re: Boxed MCU with RS-232 PortDavid Brown
||    ||   |||`- Re: Boxed MCU with RS-232 PortRick C
||    ||   ||`- Re: Boxed MCU with RS-232 PortRick C
||    ||   |`* Re: Boxed MCU with RS-232 PortDon Y
||    ||   `* Re: Boxed MCU with RS-232 PortDon Y
||    |`- Re: Boxed MCU with RS-232 PortHans-Bernhard Bröker
||    `* Re: Boxed MCU with RS-232 PortRick C
|`* Re: Boxed MCU with RS-232 PortHerbert Kleebauer
+- Re: Boxed MCU with RS-232 PortRick C
`* Re: Boxed MCU with RS-232 PortUwe Bonnes

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Re: Boxed MCU with RS-232 Port

<k867deFdvfuU1@mid.dfncis.de>

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From: HBBroe...@t-online.de (Hans-Bernhard Bröker)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 19:10:54 +0100
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 by: Hans-Bernhard Bröke - Fri, 24 Mar 2023 18:10 UTC

Am 24.03.2023 um 16:03 schrieb Rick C:
> On Friday, March 24, 2023 at 7:45:03 AM UTC-4, Hans-Bernhard Bröker
> wrote:
>> Am 24.03.2023 um 09:02 schrieb Rick C:

>>> That's one of the problems. Boards like Arduinos do not have
>>> RS-232 support. They have serial ports, but that's what was tried
>>> initially, with a home brew RS-232 level shifter added on a perf
>>> board.

>> Color me puzzled. Why on earth would anyone home-brew an RS232
>> level shifter, particularly for a project that could clearly afford
>> using ready-made ICs like MAX232 instead?
>
> That's what they used. I simply meant it was not a commercial
> product on a PCB. Half the units have some problem.
>
> Did you think I meant they designed their own level shifter chip?

You said you home-brewed the level shifter. How else was anybody to
interpret that?

Re: Boxed MCU with RS-232 Port

<k868b1FdvfuU2@mid.dfncis.de>

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From: HBBroe...@t-online.de (Hans-Bernhard Bröker)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 19:26:40 +0100
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 by: Hans-Bernhard Bröke - Fri, 24 Mar 2023 18:26 UTC

Am 24.03.2023 um 15:20 schrieb Theo:

> The problem is that commercial microcontroller boards like Arduinos tend to
> have TTL level serial ports (or USB ones). If you want a box holding one of
> those with some RS232 ports, you need to make a PCB with a MAX232 and a DB9,
> and an enclosure to match. Rick was trying to find a box with all that
> already done for him and drew a blank.

Of course he did. Finding that kind of box off-the-shelf was a very
long shot, IMHO.

Industrialized versions of the Raspberry Pi might have come close, but
they're more likely to offer RS485 or 422, insead of 232.

Re: Boxed MCU with RS-232 Port

<8e338f10-94f5-4dea-b122-250a3ae097a8n@googlegroups.com>

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Fri, 24 Mar 2023 18:34 UTC

On Friday, March 24, 2023 at 12:17:17 PM UTC-4, Herbert Kleebauer wrote:
> On 22.03.2023 20:18, Rick C wrote:
>
> > I was skimming the web for this again and I think I found something from Aaeon. Not sure why I didn't find this before. Maybe I did, but at that time was really looking for something with a simple CPU, rather than something to run a full OS. Beggars and choosers...
> >
> > https://eshop.aaeon.com/ultra-slim-box-pc-boxer-6405.html
> >
> > This one is $366, which is more than I'd like, but beggars... It is cheaper than the tailored unit a guy is working on for us. A sample unit doesn't work right and debugging across an ocean is not working very well. I could have this up and running in a day or something, as long as it comes
> with Linux installed.
> A lot of power consumption for such a task! An Atmel board
> would only consume about 0.4 W, for example something like
> that:
>
> https://www.ledato.de/product_info.php?products_id=33
> https://www.ledato.de/product_info.php?products_id=35
>
> The price is crazy, but there should be similar
> devices for only 1/5 of this price.

There should be many things in this world.

Re: Boxed MCU with RS-232 Port

<87tty9hoe2.fsf@nightsong.com>

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 13:42:45 -0700
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 by: Paul Rubin - Fri, 24 Mar 2023 20:42 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> This device is exactly what makes this difficult. Which pin on the
> DB9 is the data output?

The pinout is given here: https://wiki.dfrobot.com/RS232_Shield

How do you feel about using that board, with an Arduino? Digikey stocks
it, if that helps:

https://www.digikey.com/en/products/detail/dfrobot/DFR0258/6588574

How do you feel about recycling the enclosure from one of those port
selector switches discussed a while back?

Here is a Lilygo board which has an ESP32-C3 MCU and RS232 among
other things, for $17.98: https://www.lilygo.cc/products/t-rsc3

It is shipped from China so maybe doesn't fulfill requirements because
of that, but it at least shows that such a product exists.

Article about it with an Aliexpress redirect link (it is also sold
through there):

https://www.cnx-software.com/2023/01/20/lilygo-t-rsc3-esp32-c3-board-features-isolated-rs232-rs485-interfaces-5-to-24v-dc-input/

Direct Aliexpress

https://www.aliexpress.com/item/1005005136988162.html

Here is an Olimex MSP430 board with RS232 for around $32:

https://www.olimex.com/Products/MSP430/Starter/MSP430-5438-STK/

It is available at Mouser, though they only have 9 in stock right now:

https://www.mouser.com/ProductDetail/Olimex-Ltd/MSP430-5438STK?qs=BoUPAr39LHyy3j%2FN0eUzfQ%3D%3D

It is also on Digikey's site, but out of stock there.

There are more Olimex boards with RS232 that I didn't look up.

You mentioned that you didn't want to use an external FTDI cable on a
USB port. What about having an FTDI dongle inside the box, installed so
that its DB9 connector is panel mounted?

https://ftdichip.com/products/usb-com232-plus1/
https://ftdichip.com/products/db9-usb-f/

TTL to RS232 (?): https://www.sparkfun.com/products/449
Similar: https://www.waveshare.com/wiki/RS232_Board

Regarding the locations: are any in the western US?

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Fri, 24 Mar 2023 21:31 UTC

On Friday, March 24, 2023 at 4:42:55 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > This device is exactly what makes this difficult. Which pin on the
> > DB9 is the data output?
> The pinout is given here: https://wiki.dfrobot.com/RS232_Shield

You didn't answer the question. Which pin is the data output and which is the data input?

> How do you feel about using that board, with an Arduino? Digikey stocks
> it, if that helps:
>
> https://www.digikey.com/en/products/detail/dfrobot/DFR0258/6588574

Are you going to make the cable required?

> How do you feel about recycling the enclosure from one of those port
> selector switches discussed a while back?

Recycling is not a problem, as long as there is no branding on the box.

> Here is a Lilygo board which has an ESP32-C3 MCU and RS232 among
> other things, for $17.98: https://www.lilygo.cc/products/t-rsc3
>
> It is shipped from China so maybe doesn't fulfill requirements because
> of that, but it at least shows that such a product exists.
>
> Article about it with an Aliexpress redirect link (it is also sold
> through there):
>
> https://www.cnx-software.com/2023/01/20/lilygo-t-rsc3-esp32-c3-board-features-isolated-rs232-rs485-interfaces-5-to-24v-dc-input/
>
> Direct Aliexpress
>
> https://www.aliexpress.com/item/1005005136988162.html
>
> Here is an Olimex MSP430 board with RS232 for around $32:
>
> https://www.olimex.com/Products/MSP430/Starter/MSP430-5438-STK/
>
> It is available at Mouser, though they only have 9 in stock right now:
>
> https://www.mouser.com/ProductDetail/Olimex-Ltd/MSP430-5438STK?qs=BoUPAr39LHyy3j%2FN0eUzfQ%3D%3D
>
> It is also on Digikey's site, but out of stock there.
>
> There are more Olimex boards with RS232 that I didn't look up.
>
> You mentioned that you didn't want to use an external FTDI cable on a
> USB port. What about having an FTDI dongle inside the box, installed so
> that its DB9 connector is panel mounted?
>
> https://ftdichip.com/products/usb-com232-plus1/
> https://ftdichip.com/products/db9-usb-f/

Are you going to write the USB stack to run on the simple CPUs you have linked to?

> TTL to RS232 (?): https://www.sparkfun.com/products/449
> Similar: https://www.waveshare.com/wiki/RS232_Board

I don't know why you are showing all these devices.

> Regarding the locations: are any in the western US?

I don't know. Why does this matter? You won't be visiting the customer's site.

You seem to be thrashing around in looking at every little board that might or might not do the job, rather than finding one that will. The single port boards you've identified have the DB9 connector, but you don't indicate how you will split this into the two connectors required for the job.

Do you understand the requirements?

--

Rick C.

---+- Get 1,000 miles of free Supercharging
---+- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 15:35:24 -0700
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 by: Don Y - Fri, 24 Mar 2023 22:35 UTC

On 3/24/2023 8:08 AM, Rick C wrote:

>> Although for quantity 20 at these kind of price points, I might be tempted
>> to build something using dev boards, eg:
>> https://www.dfrobot.com/product-1030.html
>> and maybe a bit of 3D printing for an enclosure. For two of those boards
>> you might need to hand-patch one to use different pins, but it's not hard
>> and could be done.
>
> This device is exactly what makes this difficult. Which pin on the DB9 is the data output?

"Nominal" signal directions are specified from the standpoint of the *DTE*.
Remember that one rule and everything else falls into place. I.e., a DCE
*receives* data on the "Transmit Data" pin and transmits on the "Receive
Data" pin.

[Null Modem cables came into being because DTEs wanted to talk to DTEs.
So, *both* want to transmit on the TxD signal -- and thus need a pin
swap in the cable to connect out-to-in and in-to-out... even though
both are TxD]

DTE, by convention, use *male* connectors. That's the second thing to
remember.

Identify pin #1. Count sideways to the next pin; that will be RxD -- the
INPUT for the DTE device. The next pin will be TxD -- the OUTPUT for the
DTE device. (This for a DB9; using a DB25 changes this relative order).

It's not that hard (though folks tend to confuse themselves by getting
the frame of reference wrong -- esp when looking at UART chipsets
that want to label their pins TxD and RxD -- even if they are wired to
RxD and TxD, respectively, on the DB9, as is the case when implementing
a DCE).

Folks have historically bastardized all of these conventions -- for
"good reasons" (or, so they thought). But, a device (module) designed
for general use IN THE 21st CENTURY should have been designed with some
adherence to convention (i.e., male connector for DTE, female for DCE;
DTE transmits on TxD, DCE transmits on RxD). It's highly unlikely
that you're going to find a device that handshakes using SRTS or RLSD!

The roles of the control signals can quickly become confused as older
kit uses them in the original *interlocked* fashion of RS232C while
newer interpretations of the standard(s) have altered that behavior
(because most devices aren't as pathetically slow as 103 modems!)

[But, I think TWX, TELEX, et al. are long dead and gone]

Re: Boxed MCU with RS-232 Port

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 18:19:50 -0700
Organization: A noiseless patient Spider
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 by: Paul Rubin - Sat, 25 Mar 2023 01:19 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> You didn't answer the question. Which pin is the data output and
> which is the data input?

The transmit pin (TXD, pin 2 in that table) is the output and the
receive pin (RXD, pin 3) is the input. Since it is a female connector,
by the standard, the box is considered data communications equipment
(DCE), rather than data terminal equipment (DTR). If it was DTR, the
two pins would be switched around. Is that what you are asking? In any
case, one always has to test to be sure.

>> https://www.digikey.com/en/products/detail/dfrobot/DFR0258/6588574
> Are you going to make the cable required?

A splitter cable? I thought I posted a url to order those from.

> Recycling is not a problem, as long as there is no branding on the box.

There could be a label with your own branding, strategically placed to
cover up any existing branding, if that works for you.

> Are you going to write the USB stack to run on the simple CPUs you
> have linked to?

It exists already on some of them. I wouldn't write a new one.

>> TTL to RS232 (?): https://www.sparkfun.com/products/449
>> Similar: https://www.waveshare.com/wiki/RS232_Board
> I don't know why you are showing all these devices.

There are tons of cpus with built in UARTs

> I don't know. Why does this matter? You won't be visiting the
> customer's site.

Somebody at some point might have to do that. I hope not, but the
saying is, hope for the best and plan for the worst.

Frankly the first thing I would try is taking one of your homebrew boxes
that is known to be failing, swapping out the homemade level shifter PCB
with one of the ones linked above, and seeing if that works. Or at
least, use a scope to check the voltages coming out of the homemade PCB.

> You seem to be thrashing around in looking at every little board that
> might or might not do the job, rather than finding one that will.

It is a two step process: 1) identify possible candidates; 2) pick one.

Posting links to those boards is in part a demonstration that such
boards exist.

> The single port boards you've identified have the DB9 connector, but
> you don't indicate how you will split this into the two connectors
> required for the job. Do you understand the requirements?

I believe so. There are premade splitter cables that separate pins 2
and 3 from a DB9 into two more DB9's, or such a thing can be made, or
(preferable) one can use a CPU with two serial ports (or USB split into
two ports). The splitter cable can be inside the box since IIRC you
don't want it flopping around on the outside. Then the two DB9's would
be on the rear panel.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Sat, 25 Mar 2023 01:21 UTC

On Friday, March 24, 2023 at 6:35:39 PM UTC-4, Don Y wrote:
> On 3/24/2023 8:08 AM, Rick C wrote:
>
> >> Although for quantity 20 at these kind of price points, I might be tempted
> >> to build something using dev boards, eg:
> >> https://www.dfrobot.com/product-1030.html
> >> and maybe a bit of 3D printing for an enclosure. For two of those boards
> >> you might need to hand-patch one to use different pins, but it's not hard
> >> and could be done.
> >
> > This device is exactly what makes this difficult. Which pin on the DB9 is the data output?
> "Nominal" signal directions are specified from the standpoint of the *DTE*.
> Remember that one rule and everything else falls into place. I.e., a DCE
> *receives* data on the "Transmit Data" pin and transmits on the "Receive
> Data" pin.
>
> [Null Modem cables came into being because DTEs wanted to talk to DTEs.
> So, *both* want to transmit on the TxD signal -- and thus need a pin
> swap in the cable to connect out-to-in and in-to-out... even though
> both are TxD]
>
> DTE, by convention, use *male* connectors. That's the second thing to
> remember.
>
> Identify pin #1. Count sideways to the next pin; that will be RxD -- the
> INPUT for the DTE device. The next pin will be TxD -- the OUTPUT for the
> DTE device. (This for a DB9; using a DB25 changes this relative order).
>
> It's not that hard (though folks tend to confuse themselves by getting
> the frame of reference wrong -- esp when looking at UART chipsets
> that want to label their pins TxD and RxD -- even if they are wired to
> RxD and TxD, respectively, on the DB9, as is the case when implementing
> a DCE).
>
> Folks have historically bastardized all of these conventions -- for
> "good reasons" (or, so they thought). But, a device (module) designed
> for general use IN THE 21st CENTURY should have been designed with some
> adherence to convention (i.e., male connector for DTE, female for DCE;
> DTE transmits on TxD, DCE transmits on RxD). It's highly unlikely
> that you're going to find a device that handshakes using SRTS or RLSD!
>
> The roles of the control signals can quickly become confused as older
> kit uses them in the original *interlocked* fashion of RS232C while
> newer interpretations of the standard(s) have altered that behavior
> (because most devices aren't as pathetically slow as 103 modems!)
>
> [But, I think TWX, TELEX, et al. are long dead and gone]

Excellent Don. Now, please tell me which unit is the DCE and which is the DTE? Or better yet, just answer the question asked, on this device, which pin on the DB9 connector is the data output and which is the data input?

--

Rick C.

---++ Get 1,000 miles of free Supercharging
---++ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 18:22:38 -0700
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 by: Paul Rubin - Sat, 25 Mar 2023 01:22 UTC

Paul Rubin <no.email@nospam.invalid> writes:
> (DCE), rather than data terminal equipment (DTR). If it was DTR, the
> two pins would be switched around.

Sorry I meant DTE, not DTR. DTR is one of the signal pins. I believe I
got the assignments right for DCE but maybe not. Anyway there are only
two possibilities, and it's very easy to get stuff switched around
someplace, so one always has to check.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Sat, 25 Mar 2023 01:34 UTC

On Friday, March 24, 2023 at 9:19:59 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > You didn't answer the question. Which pin is the data output and
> > which is the data input?
> The transmit pin (TXD, pin 2 in that table) is the output and the
> receive pin (RXD, pin 3) is the input. Since it is a female connector,
> by the standard, the box is considered data communications equipment
> (DCE), rather than data terminal equipment (DTR). If it was DTR, the
> two pins would be switched around. Is that what you are asking? In any
> case, one always has to test to be sure.

You are providing links to hardware. I'm asking you which pin is data out and which pin is data in? This is a very simple question, no?

> >> https://www.digikey.com/en/products/detail/dfrobot/DFR0258/6588574
> > Are you going to make the cable required?
> A splitter cable? I thought I posted a url to order those from.

Do you know if that splitter will work for this application? I don't see the link. How many messages back, or how many days/weeks ago was that? You posted a lot of links in the message I replied to.

> > Recycling is not a problem, as long as there is no branding on the box.
> There could be a label with your own branding, strategically placed to
> cover up any existing branding, if that works for you.
> > Are you going to write the USB stack to run on the simple CPUs you
> > have linked to?
> It exists already on some of them. I wouldn't write a new one.

Can't use a USB dongle if there's no USB software.

> >> TTL to RS232 (?): https://www.sparkfun.com/products/449
> >> Similar: https://www.waveshare.com/wiki/RS232_Board
> > I don't know why you are showing all these devices.
> There are tons of cpus with built in UARTs

Having a UART is not sufficient. The interface needs to be a DB9 male, RS-232 voltage levels. One connector for the input data, and one connector for the output data.

> > I don't know. Why does this matter? You won't be visiting the
> > customer's site.
> Somebody at some point might have to do that. I hope not, but the
> saying is, hope for the best and plan for the worst.

That is far outside your concern.

> Frankly the first thing I would try is taking one of your homebrew boxes
> that is known to be failing, swapping out the homemade level shifter PCB
> with one of the ones linked above, and seeing if that works. Or at
> least, use a scope to check the voltages coming out of the homemade PCB.
> > You seem to be thrashing around in looking at every little board that
> > might or might not do the job, rather than finding one that will.
> It is a two step process: 1) identify possible candidates; 2) pick one.

Have you picked one yet?

> Posting links to those boards is in part a demonstration that such
> boards exist.

I've never needed convincing that these boards exist.

> > The single port boards you've identified have the DB9 connector, but
> > you don't indicate how you will split this into the two connectors
> > required for the job. Do you understand the requirements?
> I believe so. There are premade splitter cables that separate pins 2
> and 3 from a DB9 into two more DB9's, or such a thing can be made, or
> (preferable) one can use a CPU with two serial ports (or USB split into
> two ports). The splitter cable can be inside the box since IIRC you
> don't want it flopping around on the outside. Then the two DB9's would
> be on the rear panel.

Does the splitter cable run a signal to pins 2 and 3 on both cables? I've yet to find one that connects to pin 2 on one connector and pin 3 on the other connector, leaving the other pins 2 and 3 unconnected.

I think you will find the splitter cable will need to be a custom design. It's probably easier to just use a CPU without a DB9 and build a cable to run from the header to the two DB9s on the box. But then you will need a CPU card with RS232 level shifters.

This is why I don't want to do the design. It's messy and far too much work for something so simple.

--

Rick C.

--+-- Get 1,000 miles of free Supercharging
--+-- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 19:21:17 -0700
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 by: Don Y - Sat, 25 Mar 2023 02:21 UTC

On 3/24/2023 6:21 PM, Rick C wrote:
> On Friday, March 24, 2023 at 6:35:39 PM UTC-4, Don Y wrote:
>> On 3/24/2023 8:08 AM, Rick C wrote:
>>
>>>> Although for quantity 20 at these kind of price points, I might be tempted
>>>> to build something using dev boards, eg:
>>>> https://www.dfrobot.com/product-1030.html
>>>> and maybe a bit of 3D printing for an enclosure. For two of those boards
>>>> you might need to hand-patch one to use different pins, but it's not hard
>>>> and could be done.
>>>
>>> This device is exactly what makes this difficult. Which pin on the DB9 is the data output?
>> "Nominal" signal directions are specified from the standpoint of the *DTE*.
>> Remember that one rule and everything else falls into place. I.e., a DCE
>> *receives* data on the "Transmit Data" pin and transmits on the "Receive
>> Data" pin.
>>
>> [Null Modem cables came into being because DTEs wanted to talk to DTEs.
>> So, *both* want to transmit on the TxD signal -- and thus need a pin
>> swap in the cable to connect out-to-in and in-to-out... even though
>> both are TxD]
>>
>> DTE, by convention, use *male* connectors. That's the second thing to
>> remember.
>>
>> Identify pin #1. Count sideways to the next pin; that will be RxD -- the
>> INPUT for the DTE device. The next pin will be TxD -- the OUTPUT for the
>> DTE device. (This for a DB9; using a DB25 changes this relative order).
>>
>> It's not that hard (though folks tend to confuse themselves by getting
>> the frame of reference wrong -- esp when looking at UART chipsets
>> that want to label their pins TxD and RxD -- even if they are wired to
>> RxD and TxD, respectively, on the DB9, as is the case when implementing
>> a DCE).
>>
>> Folks have historically bastardized all of these conventions -- for
>> "good reasons" (or, so they thought). But, a device (module) designed
>> for general use IN THE 21st CENTURY should have been designed with some
>> adherence to convention (i.e., male connector for DTE, female for DCE;
>> DTE transmits on TxD, DCE transmits on RxD). It's highly unlikely
>> that you're going to find a device that handshakes using SRTS or RLSD!
>>
>> The roles of the control signals can quickly become confused as older
>> kit uses them in the original *interlocked* fashion of RS232C while
>> newer interpretations of the standard(s) have altered that behavior
>> (because most devices aren't as pathetically slow as 103 modems!)
>>
>> [But, I think TWX, TELEX, et al. are long dead and gone]
>
> Excellent Don. Now, please tell me which unit is the DCE and which is the DTE? Or better yet, just answer the question asked, on this device, which pin on the DB9 connector is the data output and which is the data input?

"Nominal" signal directions are specified from the standpoint of the *DTE*.
Remember that one rule and everything else falls into place. I.e., a DCE
*receives* data on the "Transmit Data" pin and transmits on the "Receive
Data" pin.

DTE, by convention, use *male* connectors. That's the second thing to remember.

Re: Boxed MCU with RS-232 Port

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From: no.em...@nospam.invalid (Paul Rubin)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 19:43:57 -0700
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 by: Paul Rubin - Sat, 25 Mar 2023 02:43 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> You are providing links to hardware. I'm asking you which pin is data
> out and which pin is data in? This is a very simple question, no?

Didn't I answer? I wrote:

>> The transmit pin (TXD, pin 2 in that table) is the output and the
>> receive pin (RXD, pin 3) is the input.

Pin 2 = data out, pin 3 = data in. Is something missing from that
answer? There is a possibility that it is wrong and that the two are
switched, but that would show up immediately during testing.

>> A splitter cable? I thought I posted a url to order those from.
> Do you know if that splitter will work for this application?

It sounded to me like it should, but part of the task is to put the
stuff together and test it. Anyway I think it is better to use a board
with two uarts. I checked, and the Arduino Leonardo has two, so it
sounds like that is a suitable board if you want to use the Arduino
approach.

> Can't use a USB dongle if there's no USB software.
The USB software is present in the boards that have USB host ports.

>> >> TTL to RS232 (?): https://www.sparkfun.com/products/449
>> >> Similar: https://www.waveshare.com/wiki/RS232_Board
>> > I don't know why you are showing all these devices.
>> There are tons of cpus with built in UARTs
>
> Having a UART is not sufficient. The interface needs to be a DB9
> male, RS-232 voltage levels. One connector for the input data, and
> one connector for the output data.

Right, that is the purpose of those boards that I linked. To convert
TTL levels to RS232 levels. You connect the UART to the level converter
board. That is pretty much the same thing that you already did with the
homemade MAX232(?) PCB, thus the idea of swapping in this other board
and seeing if it works where your existing one doesn't.

> That is far outside your concern.

I am glad to hear this. So what happens if I ship you boxes that I've
tested on my bench and that supply the right voltages as shown on a
scope, but only half of them work at the customer site, like with your
boards? Who is responsible?

> Have you picked one yet?

The Leonardo looks good to me but obviously I would want to test an
evaluation unit before settling on it.

> Does the splitter cable run a signal to pins 2 and 3 on both cables?
> I've yet to find one that connects to pin 2 on one connector and pin 3
> on the other connector, leaving the other pins 2 and 3 unconnected.

I would have to check that. However, disconnecting pin 2 or 3 can in a
cable like that can be done with a wire cutter.

> I think you will find the splitter cable will need to be a custom
> design. It's probably easier to just use a CPU without a DB9 and
> build a cable to run from the header to the two DB9s on the box. But
> then you will need a CPU card with RS232 level shifters.

The suggestion further up is to use that level shifter card.

> This is why I don't want to do the design. It's messy and far too
> much work for something so simple.

Yes, that's why nobody else wanted to do it either until you mentioned a
figure of $300 per box. That is enough to cover the necessary amount of
derping around that always afflicts a project like this. You've done a
lot more hardware stuff than I have, so I shouldn't be the one who has
to explain that.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Sat, 25 Mar 2023 03:01 UTC

On Friday, March 24, 2023 at 10:44:06 PM UTC-4, Paul Rubin wrote:
> Rick C <gnuarm.del...@gmail.com> writes:
> > You are providing links to hardware. I'm asking you which pin is data
> > out and which pin is data in? This is a very simple question, no?
> Didn't I answer? I wrote:
>
> >> The transmit pin (TXD, pin 2 in that table) is the output and the
> >> receive pin (RXD, pin 3) is the input.
> Pin 2 = data out, pin 3 = data in. Is something missing from that
> answer? There is a possibility that it is wrong and that the two are
> switched, but that would show up immediately during testing.
> >> A splitter cable? I thought I posted a url to order those from.
> > Do you know if that splitter will work for this application?
> It sounded to me like it should, but part of the task is to put the
> stuff together and test it.

Yeah, that's just what engineers do. They throw some stuff together and test it, over and over, rather than actually understanding the requirements.

I'm trying to get you to understand the issues, but you just aren't getting it. I don't know how a cable I have no info on is wired. But if pin 3 on the CPU connector goes to pin 2 on both of the cable connectors, then it's not likely to work properly is it? Two drivers on the same pin sound like a bad idea to me.

> Anyway I think it is better to use a board
> with two uarts. I checked, and the Arduino Leonardo has two, so it
> sounds like that is a suitable board if you want to use the Arduino
> approach.

Does it have RS-232 driver chips?

> > Can't use a USB dongle if there's no USB software.
> The USB software is present in the boards that have USB host ports.

I would hope so. Do any of the boards you are talking about have USB host ports? Typically the small CPU boards use a USB to serial port chip to support bootloading, with no drivers on the CPU to host USB.

> >> >> TTL to RS232 (?): https://www.sparkfun.com/products/449
> >> >> Similar: https://www.waveshare.com/wiki/RS232_Board
> >> > I don't know why you are showing all these devices.
> >> There are tons of cpus with built in UARTs
> >
> > Having a UART is not sufficient. The interface needs to be a DB9
> > male, RS-232 voltage levels. One connector for the input data, and
> > one connector for the output data.
> Right, that is the purpose of those boards that I linked. To convert
> TTL levels to RS232 levels. You connect the UART to the level converter
> board. That is pretty much the same thing that you already did with the
> homemade MAX232(?) PCB, thus the idea of swapping in this other board
> and seeing if it works where your existing one doesn't.
> > That is far outside your concern.
> I am glad to hear this. So what happens if I ship you boxes that I've
> tested on my bench and that supply the right voltages as shown on a
> scope, but only half of them work at the customer site, like with your
> boards? Who is responsible?

I think that is something we can worry about later. So far, I'm not sure you can produce any boxes.

> > Have you picked one yet?
> The Leonardo looks good to me but obviously I would want to test an
> evaluation unit before settling on it.
> > Does the splitter cable run a signal to pins 2 and 3 on both cables?
> > I've yet to find one that connects to pin 2 on one connector and pin 3
> > on the other connector, leaving the other pins 2 and 3 unconnected.
> I would have to check that. However, disconnecting pin 2 or 3 can in a
> cable like that can be done with a wire cutter.
> > I think you will find the splitter cable will need to be a custom
> > design. It's probably easier to just use a CPU without a DB9 and
> > build a cable to run from the header to the two DB9s on the box. But
> > then you will need a CPU card with RS232 level shifters.
> The suggestion further up is to use that level shifter card.
> > This is why I don't want to do the design. It's messy and far too
> > much work for something so simple.
> Yes, that's why nobody else wanted to do it either until you mentioned a
> figure of $300 per box. That is enough to cover the necessary amount of
> derping around that always afflicts a project like this. You've done a
> lot more hardware stuff than I have, so I shouldn't be the one who has
> to explain that.

When you get the details worked out, and wish to discuss a price, let me know through email.

Thanks

--

Rick C.

--+-+ Get 1,000 miles of free Supercharging
--+-+ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Fri, 24 Mar 2023 21:18:35 -0700
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 by: Paul Rubin - Sat, 25 Mar 2023 04:18 UTC

Rick C <gnuarm.deletethisbit@gmail.com> writes:
> I'm trying to get you to understand the issues, but you just aren't
> getting it. I don't know how a cable I have no info on is wired. But
> if pin 3 on the CPU connector goes to pin 2 on both of the cable
> connectors, then it's not likely to work properly is it? Two drivers
> on the same pin sound like a bad idea to me.

Again there is a 3 step process going on: 1) note that a product of this
sort exists, without remembering too much detail about it. 2) find the
product description page again, and this time study it carefully
including the pin diagrams, to develop a theory of whether it does the
right thing and which pins to connect or disconnect. 3) actually buy
the cable and test the theory.

Right now we are at step 1. I think it is best to avoid the whole thing
though. The approach of splitting the pins out from a single port is
too kludgy, if it is at all practical to use two ports.

> [Arduino Leonardo] Does it have RS-232 driver chips?

No it does not. That is why I linked those level shifter cards.

> I would hope so. Do any of the boards you are talking about have USB
> host ports?

The ESP32-S2 has it. Here are the API docs:

https://docs.espressif.com/projects/esp-idf/en/latest/esp32s2/api-reference/peripherals/usb_host.html

The CDC (communication device class) software is here:

https://github.com/espressif/esp-idf/tree/master/examples/peripherals/usb/host/cdc/cdc_acm_vcp

It looks like a potential pain in the neck to use. I currently have an
Adafruit Feather board with that chip so maybe I will try it.

The chip also supports wifi and bluetooth, fwiw. The software stacks
for both of those are way more complicated than USB.

> When you get the details worked out, and wish to discuss a price, let
> me know through email.

OK.

Re: Boxed MCU with RS-232 Port

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From: gneun...@comcast.net (George Neuner)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sat, 25 Mar 2023 21:42:12 -0400
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 by: George Neuner - Sun, 26 Mar 2023 01:42 UTC

On Fri, 24 Mar 2023 18:21:21 -0700 (PDT), Rick C
<gnuarm.deletethisbit@gmail.com> wrote:

>Excellent Don. Now, please tell me which unit is the DCE and which is
>the DTE? Or better yet, just answer the question asked, on this
>device, which pin on the DB9 connector is the data output and which
>is the data input?

"Terminal Equipment" (TE) vs "Communications Equipment" (CE).

DTE is the computer (terminal), DCE is the modem. To adhere to the
RS-232 conventions, your external device has to be "communications
equipment".

Don explained the cables and how the signaling works. DTE transmits on
TxD, and receives on RxD. DCE does the reverse. Which physical pins
these are on depends on the form factor: DB9 or DB25.

RS-232 pinout diagrams are very easy to find. Try Google.

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Sun, 26 Mar 2023 02:26 UTC

On Saturday, March 25, 2023 at 9:42:21 PM UTC-4, George Neuner wrote:
> On Fri, 24 Mar 2023 18:21:21 -0700 (PDT), Rick C
> <gnuarm.del...@gmail.com> wrote:
>
> >Excellent Don. Now, please tell me which unit is the DCE and which is
> >the DTE? Or better yet, just answer the question asked, on this
> >device, which pin on the DB9 connector is the data output and which
> >is the data input?
> "Terminal Equipment" (TE) vs "Communications Equipment" (CE).
>
> DTE is the computer (terminal), DCE is the modem. To adhere to the
> RS-232 conventions, your external device has to be "communications
> equipment".
>
> Don explained the cables and how the signaling works. DTE transmits on
> TxD, and receives on RxD. DCE does the reverse. Which physical pins
> these are on depends on the form factor: DB9 or DB25.
>
> RS-232 pinout diagrams are very easy to find. Try Google.

You are confused. I don't need any information about RS-232. Everything you are talking about is irrelevant. Virtually NO ONE uses RS-232 to connect DCE to DTE. They simply are tying together two devices that wish to use asynch serial at RS-232 voltage levels.

But neither you nor Don seem to understand that. I was trying to lead Don to this conclusion by asking pointed questions, but that failed. You, however, seem to have the same problem Don does.

I often have this problem with people who don't actually understand how RS-232 is used. There are people who view the world through data sheets and specification standards. Then there's the real world, where you have to toss out some of that, and ask questions like, "Which pin is output and which pin is input?" If the person you are talking to gives you anything other than a pin number, you are talking to the wrong person.

Engineers design stuff. Technicians figure out how to make it work.

--

Rick C.

--++- Get 1,000 miles of free Supercharging
--++- Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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From: jj...@franjam.org.uk (Jim Jackson)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 18:27:08 -0000 (UTC)
Organization: A noiseless patient Spider
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 by: Jim Jackson - Sun, 26 Mar 2023 18:27 UTC

On 2023-03-26, Rick C <gnuarm.deletethisbit@gmail.com> wrote:
>
> I often have this problem with people who don't actually understand
> how RS-232 is used. There are people who view the world through data
> sheets and specification standards. Then there's the real world,
> where you have to toss out some of that, and ask questions like,
> "Which pin is output and which pin is input?" If the person you are
> talking to gives you anything other than a pin number, you are talking
> to the wrong person.

Many years ago I often had to connect up gear with RS232 interfaces, and
it was a pain, as there was often no manual for the gear or the manual
was badly written and the author used the RS232 "standard" terms in a
cavalier way.

So I used an RS232 breakout box to try and identify RXD and TXD, and
what the various pins did, and what had to be strapped to what to get
either end to speak! Oh happy days - NOT!

Good luck with the project.

Re: Boxed MCU with RS-232 Port

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From: dp...@tgi-sci.com (Dimiter_Popoff)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 22:24:49 +0300
Organization: TGI
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 by: Dimiter_Popoff - Sun, 26 Mar 2023 19:24 UTC

Hard to believe the long fossilized RS-232 horse can get all that
beating again...
Next thing let's beat the baud rate detection? :D

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 13:23:10 -0700
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 by: Don Y - Sun, 26 Mar 2023 20:23 UTC

On 3/25/2023 6:42 PM, George Neuner wrote:
> On Fri, 24 Mar 2023 18:21:21 -0700 (PDT), Rick C
> <gnuarm.deletethisbit@gmail.com> wrote:
>
>> Excellent Don. Now, please tell me which unit is the DCE and which is
>> the DTE? Or better yet, just answer the question asked, on this
>> device, which pin on the DB9 connector is the data output and which
>> is the data input?
>
> "Terminal Equipment" (TE) vs "Communications Equipment" (CE).
>
> DTE is the computer (terminal), DCE is the modem. To adhere to the
> RS-232 conventions, your external device has to be "communications
> equipment".
>
> Don explained the cables and how the signaling works. DTE transmits on
> TxD, and receives on RxD. DCE does the reverse. Which physical pins
> these are on depends on the form factor: DB9 or DB25.
>
> RS-232 pinout diagrams are very easy to find. Try Google.

Rick doesn't understand how the Standard is interpreted solely as
"guidance", in the real world. The idea that someone ELSE could
examine *his* choice of device from *his* chosen vendor and
comment, in any meaningful way, suggests a naivite that's
beyond laughable.

APC uses a DB9 that *seems* to implement RS232. Yet, if you
wire it to a nominal mate, you'll find the UPS will shutdown.
Because THEY have repurposed one of the modem control signals
as a "shutdown" signal. Ooops!

Is APC (Schneider Electric) a dubious little garage shop
selling products that likely have limited lifetimes? I.e.,
you want to talk to an APC UPS, you learn how APC expects
the port to be wired and used. If this is unacceptable
to you, you find another UPS vendor and hope for something
better.

Having a pinout tells you very little more than which
signals you can "safely" connect together; it tells you
nothing about the function of the signal, the protocol or
content. E.g., using RLSD as a pacing signal (WTF??)
The choice of UART gives a *hint* as to how responsive the
software (firmware, drivers, HAL, etc.) will be to signalling
conventions and message latency.

If I twiddle a "handshaking" (misnomer) signal, how quickly
will the other party stop transmitting? How many *more*
characters must I be prepared to receive as it's output
buffer, holding register and ISR empties and it reacts to
my notification? What's the worst-case latency on the ISR
being handled IN THAT BOX? How slow have *I* been to
recognize that I'm backlogged? Am I (ISR) reacting to a
character received many character-times earlier?

If I send an in-band signal to convey the same information,
how long before that reaches the wire? And, propagates
up the receiving stack to a point where the other device
can recognize my "signal"? Then, all of the above questions
repeat, again.

Will in-band signals be accepted if the link relies on hardware
handshaking (pacing) signals? Will they be elided if encountered
in messages EVEN WHEN NOT CONFIGURED AS SIGNALS? Which in-band
characters will be used (^S and ^Q may be the most common but they
are not immutable choices)? Will ANY received character (IXANY)
suffice to signal resumption of transmission is allowed?

What if a device misses a flow control signal? How can I
*reliably* restart it (given that I may not know what it's doing)
without contaminating the data stream?

Are they pacing signals or handshaking signals (most folks
have never had to deal with the original Standard's
implementation!)?

Does the device send two stop bits but only check for one?
Is parity generated? Is received parity *checked* (or just
an extra bit-time in the character frame)? Does the device
send/acknowledge long BREAKs? Does it use /n, /r, either,
or both as a line delimiter? Is the line buffered before
delivery to the application layer?

Does it expect additional delay at \r? \n? \t? \b? \f? \v?
Does it reliably support every data rate advertised? Who
chose the cable -- and how? What is the impact on the device's
overall functionality of increasing data rates? Of mismatched
rates?

Repeat all of this from the vantage point of the other device;
how will *it* expect ME to behave? And, how will it react if
I MISbehave? (will an input buffer overrun because it was naively
sized for fixed-length messages?) How will *I* react if *it* misbehaves?

PCs are ubiquitous. Yet, have you ever seen any of these issues
quantified and published in a form that you could rely on in a
design? If I use one of the modem control signals to turn around
a bidirectional transceiver, how do I know that the last character
has *cleared* it AT THE TIME THE SIGNAL ASSERTS? How do I guarantee
that the code runs on some other PC, equivalently??

If you are coding on bare metal, you can answer these questions from
YOUR end of the wire. If you are relying on a COTS device with
"drivers" in place, then good luck finding the information (unless
you can examine the schematics and source code and reverse engineer
the limits of their implementation -- or, replace it entirely).

People expecting to have an answer to these questions before
*touching* a COTS product are woefully naive. People expecting
others to do their work FOR them are just opportunistic cads.
(Or, profoundly incompetent)

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 13:23:15 -0700
Organization: A noiseless patient Spider
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 by: Don Y - Sun, 26 Mar 2023 20:23 UTC

On 3/26/2023 11:27 AM, Jim Jackson wrote:
> Many years ago I often had to connect up gear with RS232 interfaces, and
> it was a pain, as there was often no manual for the gear or the manual
> was badly written and the author used the RS232 "standard" terms in a
> cavalier way.

Folks who haven't designed communications equipment where RS232 (in its
various bastardized forms) don't understand that commenting on a product
chosen (seemingly) at random from a producer of unknown character is
pure folly. Simply because the folks who design said pieces of
kit are operating often in ignorance -- trying to make a device that
mates with X instead of a device that conforms to a standard.

This is a common problem when folks try to "bottom feed".

> So I used an RS232 breakout box to try and identify RXD and TXD, and
> what the various pins did, and what had to be strapped to what to get
> either end to speak! Oh happy days - NOT!

There were "magic (active) cables" produced years ago that would,
automatically, adapt to common pinout incompatibilities. But, "common"
is the operative word, here. And, if you were in a market where
*many* of the pins on a DB25 were active, they were just toy solutions.

Just getting the pinout to *appear* correct is only part of the story.
You also need to know how they have implemented the signaling protocol
and the timing thereof (see my reply to George, upthread)

I have encountered devices made by "established companies" that use
all sorts of different signaling schemes as well as pinouts. As
I mentioned in an earlier post, seeing SRTS used for flow control, or
RLSD, etc. I'm sure there's a reason they made these bastardizations
but, regardless, I had to live with it as the vendor isn't going to
"fix" his implementation just to satisfy my beliefs.

As I have had to design many such devices, over the years, to interact
with many *other* devices (they having undisclosed design goals), I
quickly learned to accumulate a set of "widgets" that would allow me
to quickly make common signal swaps. Then, once each end of the link
looked like a DCE or DTE, a straight-through cable solved the ELECTRICAL
problem.

[E.g., I can understand APC's bastardization, below. Almost. Yet,
feel they could have implemented the feature set in a more compatible
way...]

I build these into connector shells that are designed to support a
pair of back-to-back connectors (DB9 or 25) and then affix a label
telling me the device that it is intended to normalize (e.g., I have
one at my feet that "fixes" APC's UPS serial port) *or* the function
it is intended to perform (gender change, NULL modem, NULL 'terminal'!,
etc.)

An early employer (specializing in comms kit!) had a huge box
full of assorted (and undocumented) cables. One of the first
chores on any project was finding a suitable cable to mate
to the device in question. This involved untangling dozens of
cords and *trying* each, in turn, until some signs of life
appeared. Then, refining the selection.

I pitched the idea of the small (2"x2") widgets paired with
a straight-through cable. Discard the box of random wire
and keep a shoebox full of the little widgets -- and ONLY
straight through, M-F cables. Sometimes I have to stack
a few "widgets" to get the requisite signal pairing.
But, then know how to make a new widget that is tailored
to THIS device (and labeled as such)

> Good luck with the project.

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 13:32:41 -0700
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 by: Don Y - Sun, 26 Mar 2023 20:32 UTC

On 3/26/2023 1:23 PM, Don Y wrote:
> I build these into connector shells that are designed to support a
> pair of back-to-back connectors (DB9 or 25) and then affix a label
> telling me the device that it is intended to normalize (e.g., I have
> one at my feet that "fixes" APC's UPS serial port) *or* the function
> it is intended to perform (gender change, NULL modem, NULL 'terminal'!,
> etc.)

This is the APC widget mentioned:
<https://mega.nz/file/J35SBBob#FtQznCDovhBZHJdA5OspHdMo6_DiDMjQwtCqnh3Oa54>

By (my) convention, the named device ("UPS") is located at the
connector from which the label can be read (i.e., the connector
to the right).

The jack screws -- in the context of that device -- act as a further
hint.

If I want to know what's inside, I have to look up the schematic
for the widget -- unless the function is obvious (e.g., gender
change).

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 13:37:39 -0700
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 by: Don Y - Sun, 26 Mar 2023 20:37 UTC

On 3/25/2023 7:26 PM, Rick C wrote:
> Engineers design stuff. Technicians figure out how to make it work.

And you apparently do neither. <frown>

Re: Boxed MCU with RS-232 Port

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From: blockedo...@foo.invalid (Don Y)
Newsgroups: comp.arch.embedded
Subject: Re: Boxed MCU with RS-232 Port
Date: Sun, 26 Mar 2023 13:52:41 -0700
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 by: Don Y - Sun, 26 Mar 2023 20:52 UTC

On 3/26/2023 1:32 PM, Don Y wrote:
> On 3/26/2023 1:23 PM, Don Y wrote:
>> I build these into connector shells that are designed to support a
>> pair of back-to-back connectors (DB9 or 25) and then affix a label
>> telling me the device that it is intended to normalize (e.g., I have
>> one at my feet that "fixes" APC's UPS serial port) *or* the function
>> it is intended to perform (gender change, NULL modem, NULL 'terminal'!,
>> etc.)
>
> This is the APC widget mentioned:
> <https://mega.nz/file/J35SBBob#FtQznCDovhBZHJdA5OspHdMo6_DiDMjQwtCqnh3Oa54>

And this is the COTS *PC* that I use as a name server:
<https://mega.nz/file/Fi4hEACJ#YgVZ5tdZBjTcwW76gXC2vdgv5M6u4lTpUDAwu53Z9n8>

Note the *two* serial ports (DTE as the standard dictates), 100BaseT
network connection (it's just a name server, it doesn't need to
have high throughput), PS/2 keyboard and VGA (cuz it's a PC!),
wifi and USB. The four mounting holes visible are the VESA standard
(I have these mounted between my monitor and support arm)

As an ISA PC, it will run damn near any OS intended for such
a platform (I run NetBSD on this box). So, all of the PC hosted
AND TARGETED tools are available (I have a LFC monitor wired to
one of the serial ports to discipline my time service as that
was easier/cheaper to implement than any other solution!).

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Mon, 27 Mar 2023 02:11 UTC

On Sunday, March 26, 2023 at 2:27:14 PM UTC-4, Jim Jackson wrote:
> On 2023-03-26, Rick C <gnuarm.del...@gmail.com> wrote:
> >
> > I often have this problem with people who don't actually understand
> > how RS-232 is used. There are people who view the world through data
> > sheets and specification standards. Then there's the real world,
> > where you have to toss out some of that, and ask questions like,
> > "Which pin is output and which pin is input?" If the person you are
> > talking to gives you anything other than a pin number, you are talking
> > to the wrong person.
> Many years ago I often had to connect up gear with RS232 interfaces, and
> it was a pain, as there was often no manual for the gear or the manual
> was badly written and the author used the RS232 "standard" terms in a
> cavalier way.
>
> So I used an RS232 breakout box to try and identify RXD and TXD, and
> what the various pins did, and what had to be strapped to what to get
> either end to speak! Oh happy days - NOT!
>
> Good luck with the project.

Fortunately, this effort only uses TX and GND on one port and RX and GND on the other port. I don't care what the TX and RX pins are called, one is input, the other output and we just need to connect the input to the device that is sending the data and connect the output to the device that is receiving data. All this has already been worked out and a prototype was built. Unfortunately there is some problem that results in a hung unit from time to time. That developer doesn't have the time to mess with it, so we are looking elsewhere. But the pin assignments are not a problem, just people's perspective on the issue.

--

Rick C.

--+++ Get 1,000 miles of free Supercharging
--+++ Tesla referral code - https://ts.la/richard11209

Re: Boxed MCU with RS-232 Port

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Subject: Re: Boxed MCU with RS-232 Port
From: gnuarm.d...@gmail.com (Rick C)
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 by: Rick C - Mon, 27 Mar 2023 02:22 UTC

On Sunday, March 26, 2023 at 4:25:49 PM UTC-4, Don Y wrote:
> On 3/26/2023 11:27 AM, Jim Jackson wrote:
> > Many years ago I often had to connect up gear with RS232 interfaces, and
> > it was a pain, as there was often no manual for the gear or the manual
> > was badly written and the author used the RS232 "standard" terms in a
> > cavalier way.
> Folks who haven't designed communications equipment where RS232 (in its
> various bastardized forms) don't understand that commenting on a product
> chosen (seemingly) at random from a producer of unknown character is
> pure folly. Simply because the folks who design said pieces of
> kit are operating often in ignorance -- trying to make a device that
> mates with X instead of a device that conforms to a standard.

And there is the problem. The RS-232 standard defines the interface between data terminal equipment and data communication equipment, at the data communication equipment interface. It says nothing about anything else. However, people use these voltages and so these level shifting devices, often along with the same type of connectors for many *other* applications. At that point, the RS-232 standard does not apply in a consistent way. So people are free to pick and choose the parts they want, and the parts they don't want.

The RS-232 moniker is often used, when even the voltage levels are not the same. At that point, there is nothing RS-232 about it. People are just using the term as a synonym for an async serial port.

--

Rick C.

-+--- Get 1,000 miles of free Supercharging
-+--- Tesla referral code - https://ts.la/richard11209

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