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computers / comp.sys.raspberry-pi / Re: usb-serial adapters

SubjectAuthor
* usb-serial adaptersbob prohaska
+- Re: usb-serial adaptersyeti
+* Re: usb-serial adapterscrn
|+* Re: usb-serial adaptersChris Green
||+* Re: usb-serial adaptersThe Natural Philosopher
|||`* Re: usb-serial adaptersJean-Pierre Kuypers
||| +- Re: usb-serial adaptersThe Natural Philosopher
||| `- Re: usb-serial adaptersChris Green
||+* Re: usb-serial adaptersDavid Higton
|||`* Re: usb-serial adaptersChris Green
||| `* Re: usb-serial adaptersTheo
|||  +* Re: usb-serial adaptersChris Green
|||  |`* Re: usb-serial adaptersTheo
|||  | `- Re: usb-serial adaptersAhem A Rivet's Shot
|||  +- Re: usb-serial adaptersTauno Voipio
|||  `* Re: usb-serial adaptersScott Alfter
|||   `- Re: usb-serial adaptersAhem A Rivet's Shot
||`* Re: usb-serial adaptersAnssi Saari
|| `- Re: usb-serial adaptersCharlie Gibbs
|`* Re: usb-serial adaptersTheo
| +- Re: usb-serial adaptersComputer Nerd Kev
| `- Re: usb-serial adaptersbob prohaska
+- Re: usb-serial adaptersStephen Pelc
+* usb-serial adaptersA.M. Rowsell
|`- Re: usb-serial adaptersDeloptes
`* Re: usb-serial adapters56g.1183
 `* Re: usb-serial adaptersTheo
  `* Re: usb-serial adapters56g.1183
   +* Re: usb-serial adaptersJim Jackson
   |+- Re: usb-serial adaptersThe Natural Philosopher
   |`* Re: usb-serial adapters56g.1183
   | `* Re: usb-serial adaptersJim Jackson
   |  +* Re: usb-serial adaptersMichael Schwingen
   |  |`- Re: usb-serial adaptersJim Jackson
   |  `* Re: usb-serial adapters57r.1283
   |   +- Re: usb-serial adaptersCharlie Gibbs
   |   `- Re: usb-serial adaptersJim Jackson
   `- Re: usb-serial adaptersDeloptes

Pages:12
Re: usb-serial adapters

<Rnq*5pvzz@news.chiark.greenend.org.uk>

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From: theom+n...@chiark.greenend.org.uk (Theo)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: 03 Jan 2024 12:15:35 +0000 (GMT)
Organization: University of Cambridge, England
Message-ID: <Rnq*5pvzz@news.chiark.greenend.org.uk>
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 by: Theo - Wed, 3 Jan 2024 12:15 UTC

56g.1183 <56g.1183@ztq4.net> wrote:
> In My Experience - MOST USB/SERIAL adapters work OK
> in PI/OS. I think, despite brand names, there are only
> a few actual chip-sets.
>
> While Amazon reviews are a bit suspect, still DO
> read them, with particular attention to Linux
> remarks

If you can find the chip number, that's the main thing. If there is a link
to Windows drivers, downloading them and taking a look at the .inf file is a
good clue.

> IF you get stuck having to load virtual Winders
> drivers ... then you haven't chosen wisely

There is no support for running virtual Windows serial drivers in Linux.

> Pi's can also do RS-232 directly. A bit less civil,
> but it works.

Pis can do *serial* directly, but not RS232. They only have 3.3V signal
levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
etc).

Theo

Re: usb-serial adapters

<oaicnQEyYeeZrAv4nZ2dnZfqnPSdnZ2d@earthlink.com>

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Subject: Re: usb-serial adapters
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From: 56g.1...@ztq4.net (56g.1183)
Organization: bluejay volume
Date: Wed, 3 Jan 2024 23:16:03 -0500
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 by: 56g.1183 - Thu, 4 Jan 2024 04:16 UTC

On 1/3/24 7:15 AM, Theo wrote:
> 56g.1183 <56g.1183@ztq4.net> wrote:
>> In My Experience - MOST USB/SERIAL adapters work OK
>> in PI/OS. I think, despite brand names, there are only
>> a few actual chip-sets.
>>
>> While Amazon reviews are a bit suspect, still DO
>> read them, with particular attention to Linux
>> remarks
>
> If you can find the chip number, that's the main thing. If there is a link
> to Windows drivers, downloading them and taking a look at the .inf file is a
> good clue.
>
>> IF you get stuck having to load virtual Winders
>> drivers ... then you haven't chosen wisely
>
> There is no support for running virtual Windows serial drivers in Linux.
>
>> Pi's can also do RS-232 directly. A bit less civil,
>> but it works.
>
> Pis can do *serial* directly, but not RS232. They only have 3.3V signal
> levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
> etc).

Yep ... level-shifting chips are generally needed.
The MAX3232 will do it.


https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf

If you are talking to VERY old serial devices that still
expect some plus/minus 12v or more signals then you may
have to double-up, add a MAX232 after the 3232

3.x volts IS a pain in the ass. Eventually all the old
devices will be gone and the new stuff will do 3.x or
less. However, there are still a lot of those "old devices"
still out there and still in profitable use and likely
will be for at least another 25 years.

As for converters ... I'd swear I got a USB<->232
unit working on a Pi3 ... but don't quote me on it.
I'm kinda a hardware guy, so I would have made
something with the MAX chips almost automatically.

Anyhow, peruse the usual spots, AdaFruit, SparkFun,
Seeed. They may have a canned solution.

Re: usb-serial adapters

<slrnupd928.569.jj@iridium.wf32df>

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From: jj...@franjam.org.uk (Jim Jackson)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Thu, 4 Jan 2024 12:27:52 -0000 (UTC)
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 by: Jim Jackson - Thu, 4 Jan 2024 12:27 UTC

On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:
>>
>> Pis can do *serial* directly, but not RS232. They only have 3.3V signal
>> levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
>> etc).
>
> Yep ... level-shifting chips are generally needed.
> The MAX3232 will do it.

It does more than "level shift" it also inverts the signals. It will
accept 3v or 5v logic, even though supplied from a 3.3v supply.

>
> https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf
>
> If you are talking to VERY old serial devices that still
> expect some plus/minus 12v or more signals then you may
> have to double-up, add a MAX232 after the 3232

Maybe. But not as you say. You would need a simple 3v to 5v level
shifter (so as NOT to invert the signal) then the MAX232.

> ...snip...
> Anyhow, peruse the usual spots, AdaFruit, SparkFun,
> Seeed. They may have a canned solution.

sound advice.

Re: usb-serial adapters

<un6996$3lcqq$3@dont-email.me>

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From: tnp...@invalid.invalid (The Natural Philosopher)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Thu, 4 Jan 2024 12:45:26 +0000
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 by: The Natural Philosop - Thu, 4 Jan 2024 12:45 UTC

On 04/01/2024 12:27, Jim Jackson wrote:
> On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:

>> ...snip...
>> Anyhow, peruse the usual spots, AdaFruit, SparkFun,
>> Seeed. They may have a canned solution.
>
> sound advice.

https://thepihut.com/products/serial-pizero

level conversion inbuilt

--
"When a true genius appears in the world, you may know him by this sign,
that the dunces are all in confederacy against him."

Jonathan Swift.

Re: usb-serial adapters

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Subject: Re: usb-serial adapters
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From: 56g.1...@ztq4.net (56g.1183)
Organization: bluejay volume
Date: Fri, 5 Jan 2024 01:35:55 -0500
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 by: 56g.1183 - Fri, 5 Jan 2024 06:35 UTC

On 1/4/24 7:27 AM, Jim Jackson wrote:
> On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:
>>>
>>> Pis can do *serial* directly, but not RS232. They only have 3.3V signal
>>> levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
>>> etc).
>>
>> Yep ... level-shifting chips are generally needed.
>> The MAX3232 will do it.
>
> It does more than "level shift" it also inverts the signals. It will
> accept 3v or 5v logic, even though supplied from a 3.3v supply.

Properly wired, the MAX232 can deliver "real" RS-232 ... including
the negative voltages. There IS still some equipment that expects
those kinds of signals ... albeit mostly early-80s. Some industrial
controllers of that vintage are still in use however.

Flow-control ... sticky. For RECEIVING no modern cpu/controller
is so slow that it cannot absorb such comms at even the highest
usual RS232 speeds. However those ancient devices you may be
communicating with may NOT be able to absorb the info so quickly.
Ergo you have to respect their flow-control lines. Serial comms
can be a pain in the ass. There are subtle issues.

>>
>> https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf
>>
>> If you are talking to VERY old serial devices that still
>> expect some plus/minus 12v or more signals then you may
>> have to double-up, add a MAX232 after the 3232
>
> Maybe. But not as you say. You would need a simple 3v to 5v level
> shifter (so as NOT to invert the signal) then the MAX232.

Again, depends on what you are trying to converse with.
Very old devices may expect/depend on those rather high
negative signal levels.

>> ...snip...
>> Anyhow, peruse the usual spots, AdaFruit, SparkFun,
>> Seeed. They may have a canned solution.
>
> sound advice.

These days there's often a canned fix for just a few dollars.
Kinda takes the fun out of it though :-)

Re: usb-serial adapters

<un8af1$2uk7$1@dont-email.me>

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From: delop...@gmail.com (Deloptes)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Fri, 05 Jan 2024 08:17:52 +0100
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 by: Deloptes - Fri, 5 Jan 2024 07:17 UTC

A.M. Rowsell wrote:

> There is a seller on Tindie called 8086 Consultancy that has a whole bunch
> of https://tindie.com/stores/8086net/items/ if you
> want to take a look. Lots of pi-related devices as well. But the chips you
> mentioned are still pretty much the only good choices.
> Aurelius

It was not too hard to build one with the MAX3232CPE. I even added leds
indicating the data transmission on the RX/TX pins. It works with the RPI2
and RPI4 very well. It is not isolated and protected so proper wiring is
important

Re: usb-serial adapters

<un8be4$32t0$1@dont-email.me>

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From: delop...@gmail.com (Deloptes)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
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 by: Deloptes - Fri, 5 Jan 2024 07:34 UTC

56g.1183 wrote:

> Yep ... level-shifting chips are generally needed.
> The MAX3232 will do it.
>
>
>
https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf
>

It was not too hard to build one with the MAX3232CPE. I even added leds
indicating the data transmission on the RX/TX pins. It works with the RPI2
and RPI4 very well. It is not isolated and protected so proper wiring is
important. Here are my notes on this

https://deloptes.org/articles/MAX3232CPE/Howto_RS232_TTL_MAX3232.pdf

Re: usb-serial adapters

<slrnupm048.47t.jj@iridium.wf32df>

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From: jj...@franjam.org.uk (Jim Jackson)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Sun, 7 Jan 2024 19:50:32 -0000 (UTC)
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 by: Jim Jackson - Sun, 7 Jan 2024 19:50 UTC

On 2024-01-05, 56g.1183 <56g.1183@ztq4.net> wrote:
> On 1/4/24 7:27 AM, Jim Jackson wrote:
>> On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:
>>>>
>>>> Pis can do *serial* directly, but not RS232. They only have 3.3V signal
>>>> levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
>>>> etc).
>>>
>>> Yep ... level-shifting chips are generally needed.
>>> The MAX3232 will do it.
>>
>> It does more than "level shift" it also inverts the signals. It will
>> accept 3v or 5v logic, even though supplied from a 3.3v supply.
>
>
> Properly wired, the MAX232 can deliver "real" RS-232 ... including
> the negative voltages.

The 3232 does provide the negative and positive voltages but only at
+/-5.5v Which is fine for most modern stuff, but as you say below not
for some older stuff.

> There IS still some equipment that expects
> those kinds of signals ... albeit mostly early-80s. Some industrial
> controllers of that vintage are still in use however.
>
> Flow-control ... sticky. For RECEIVING no modern cpu/controller
> is so slow that it cannot absorb such comms at even the highest
> usual RS232 speeds. However those ancient devices you may be
> communicating with may NOT be able to absorb the info so quickly.
> Ergo you have to respect their flow-control lines. Serial comms
> can be a pain in the ass. There are subtle issues.
>>>
>>> https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf
>>>
>>> If you are talking to VERY old serial devices that still
>>> expect some plus/minus 12v or more signals then you may
>>> have to double-up, add a MAX232 after the 3232
>>
>> Maybe. But not as you say. You would need a simple 3v to 5v level
>> shifter (so as NOT to invert the signal) then the MAX232.
>
> Again, depends on what you are trying to converse with.
> Very old devices may expect/depend on those rather high
> negative signal levels.

Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v
logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the
MAX232 inputs.

Re: usb-serial adapters

<slrnupokdk.5gm.news-1513678000@a-tuin.ms.intern>

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From: news-151...@discworld.dascon.de (Michael Schwingen)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: 8 Jan 2024 19:49:08 GMT
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 by: Michael Schwingen - Mon, 8 Jan 2024 19:49 UTC

On 2024-01-07, Jim Jackson <jj@franjam.org.uk> wrote:
>> Properly wired, the MAX232 can deliver "real" RS-232 ... including
>> the negative voltages.
>
> The 3232 does provide the negative and positive voltages but only at
> +/-5.5v Which is fine for most modern stuff, but as you say below not
> for some older stuff.

Which means the older stuff is broken and not really conforming to RS232 -
the signals from the '3232 & Co *are* fully RS232-compliant.

Yes, I know broken stuff exists and if you need to interface to such stuff,
you need better drivers, but the blame is on the broken equipment and not on
the MAX3232.

>> Again, depends on what you are trying to converse with.
>> Very old devices may expect/depend on those rather high
>> negative signal levels.
>
> Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v
> logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the
> MAX232 inputs.

When driving a RS232 load, the MAX232E output is specified at +-9V typical,
+-5V guaranteed minimum - not +-12 (it internally doubles the +5V supply, so
there is no way to get above 10V).

The MAX3232 output is +-5V minimum, and +-5.5V typical.

If you really need more output swing, you will have to use something like a
SN75188 (with a 3.3V -> 5V level converter, and +-13V supplies) - at
VCC=+-13.2V, these will drive +-9V guaranteed and +-10.5V typical.

With Vih=1.9V, these might even work from a 3.3V output without additional
level translation.

cu
Michael
--
Some people have no respect of age unless it is bottled.

Re: usb-serial adapters

<slrnupou1b.hb1.jj@iridium.wf32df>

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From: jj...@franjam.org.uk (Jim Jackson)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Mon, 8 Jan 2024 22:33:15 -0000 (UTC)
Organization: A noiseless patient Spider
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 by: Jim Jackson - Mon, 8 Jan 2024 22:33 UTC

On 2024-01-08, Michael Schwingen <news-1513678000@discworld.dascon.de> wrote:
> On 2024-01-07, Jim Jackson <jj@franjam.org.uk> wrote:
>>> Properly wired, the MAX232 can deliver "real" RS-232 ... including
>>> the negative voltages.
>>
>> The 3232 does provide the negative and positive voltages but only at
>> +/-5.5v Which is fine for most modern stuff, but as you say below not
>> for some older stuff.
>
> Which means the older stuff is broken and not really conforming to RS232 -
> the signals from the '3232 & Co *are* fully RS232-compliant.

Indeed, and as you say the blame is on the equipment - but in the late
80's early 90's there was a lot of crap^H^H^H^H non-conformant equipment
:-)

> Yes, I know broken stuff exists and if you need to interface to such stuff,
> you need better drivers, but the blame is on the broken equipment and not on
> the MAX3232.
>
>>> Again, depends on what you are trying to converse with.
>>> Very old devices may expect/depend on those rather high
>>> negative signal levels.
>>
>> Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v
>> logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the
>> MAX232 inputs.
>
> When driving a RS232 load, the MAX232E output is specified at +-9V typical,
> +-5V guaranteed minimum - not +-12 (it internally doubles the +5V supply, so
> there is no way to get above 10V).

Ah I mis-remembered - thanks for that.

> The MAX3232 output is +-5V minimum, and +-5.5V typical.
>
> If you really need more output swing, you will have to use something like a
> SN75188 (with a 3.3V -> 5V level converter, and +-13V supplies) - at
> VCC=+-13.2V, these will drive +-9V guaranteed and +-10.5V typical.
>
> With Vih=1.9V, these might even work from a 3.3V output without additional
> level translation.
>

cheers

Re: usb-serial adapters

<xsScnRdzl-01Fz34nZ2dnZfqnPednZ2d@earthlink.com>

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NNTP-Posting-Date: Fri, 12 Jan 2024 00:41:12 +0000
Subject: Re: usb-serial adapters
Newsgroups: comp.sys.raspberry-pi
References: <um832v$29qo9$1@dont-email.me> <Pe-cnUAvBf3ZZwn4nZ2dnZfqnPWdnZ2d@earthlink.com> <Rnq*5pvzz@news.chiark.greenend.org.uk> <oaicnQEyYeeZrAv4nZ2dnZfqnPSdnZ2d@earthlink.com> <slrnupd928.569.jj@iridium.wf32df> <CO2dndKaUNbRPgr4nZ2dnZfqnPGdnZ2d@earthlink.com> <slrnupm048.47t.jj@iridium.wf32df>
From: 57r.1...@etq5.net (57r.1283)
Organization: fiber ambience
Date: Thu, 11 Jan 2024 19:41:12 -0500
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 by: 57r.1283 - Fri, 12 Jan 2024 00:41 UTC

On 1/7/24 2:50 PM, Jim Jackson wrote:
> On 2024-01-05, 56g.1183 <56g.1183@ztq4.net> wrote:
>> On 1/4/24 7:27 AM, Jim Jackson wrote:
>>> On 2024-01-04, 56g.1183 <56g.1183@ztq4.net> wrote:
>>>>>
>>>>> Pis can do *serial* directly, but not RS232. They only have 3.3V signal
>>>>> levels, so voltage conversion needed for RS232 or another voltage (1.8V, 5V,
>>>>> etc).
>>>>
>>>> Yep ... level-shifting chips are generally needed.
>>>> The MAX3232 will do it.
>>>
>>> It does more than "level shift" it also inverts the signals. It will
>>> accept 3v or 5v logic, even though supplied from a 3.3v supply.
>>
>>
>> Properly wired, the MAX232 can deliver "real" RS-232 ... including
>> the negative voltages.
>
> The 3232 does provide the negative and positive voltages but only at
> +/-5.5v Which is fine for most modern stuff, but as you say below not
> for some older stuff.
>
>> There IS still some equipment that expects
>> those kinds of signals ... albeit mostly early-80s. Some industrial
>> controllers of that vintage are still in use however.
>>
>> Flow-control ... sticky. For RECEIVING no modern cpu/controller
>> is so slow that it cannot absorb such comms at even the highest
>> usual RS232 speeds. However those ancient devices you may be
>> communicating with may NOT be able to absorb the info so quickly.
>> Ergo you have to respect their flow-control lines. Serial comms
>> can be a pain in the ass. There are subtle issues.
>>>>
>>>> https://www.analog.com/media/en/technical-documentation/data-sheets/MAX3222-MAX3241.pdf
>>>>
>>>> If you are talking to VERY old serial devices that still
>>>> expect some plus/minus 12v or more signals then you may
>>>> have to double-up, add a MAX232 after the 3232
>>>
>>> Maybe. But not as you say. You would need a simple 3v to 5v level
>>> shifter (so as NOT to invert the signal) then the MAX232.
>>
>> Again, depends on what you are trying to converse with.
>> Very old devices may expect/depend on those rather high
>> negative signal levels.
>
> Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v
> logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the
> MAX232 inputs.

Probably true. I think the 3232 is 3.3 in/out so some kind
of level-converter would be required between it and the 232.
Cheap, or you can make yer own, but it's an extra level of
complication.

Thing is, some of that old equipment (oft industrial) IS still
out there doing its job so a Fake-to-Real RS232 (might add a
couple other RS's) converter might be a worthwhile bit of kit
to have around.

There's also the issue of the flow-control lines. While modern
stuff is fast enough to not worry about it, the old equipment
might need to signal a brief stop while you are sending to it.
Buffers were often very small back then (and processing slow).

Async is versatile, but a pain in the rump sometimes. Synchronous
serial is more civilized. However most equipment you'll ever come
across is async.

Re: usb-serial adapters

<wi0oN.145493$Wp_8.144635@fx17.iad>

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Newsgroups: comp.sys.raspberry-pi
From: cgi...@kltpzyxm.invalid (Charlie Gibbs)
Subject: Re: usb-serial adapters
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 by: Charlie Gibbs - Fri, 12 Jan 2024 01:08 UTC

On 2024-01-12, 57r.1283 <57r.1283@etq5.net> wrote:

> Async is versatile, but a pain in the rump sometimes. Synchronous
> serial is more civilized. However most equipment you'll ever come
> across is async.

Synchronous was more common in the mainframe environments of old.
It can be a real pain to set up, especially if you're trying to
get hardware from different manufacturers to talk to each other.
Synchronous protocols are better suited to sending files across
the country than characters across the room. The handshaking
overhead can easily eat up the speed advantage of losing async's
start and stop bits.

--
/~\ Charlie Gibbs | The Internet is like a big city:
\ / <cgibbs@kltpzyxm.invalid> | it has plenty of bright lights and
X I'm really at ac.dekanfrus | excitement, but also dark alleys
/ \ if you read it the right way. | down which the unwary get mugged.

Re: usb-serial adapters

<slrnuq2feg.2qg.jj@iridium.wf32df>

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From: jj...@franjam.org.uk (Jim Jackson)
Newsgroups: comp.sys.raspberry-pi
Subject: Re: usb-serial adapters
Date: Fri, 12 Jan 2024 13:25:36 -0000 (UTC)
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 by: Jim Jackson - Fri, 12 Jan 2024 13:25 UTC

On 2024-01-12, 57r.1283 <57r.1283@etq5.net> wrote:
> On 1/7/24 2:50 PM, Jim Jackson wrote:
>> Indeed, which the max232 provides, +/- 12v. But it needs driving with 5v
>> logic levels. Hence the need for the 3v-to-5v level shifters BEFORE the
>> MAX232 inputs.
>
>
> Probably true. I think the 3232 is 3.3 in/out so some kind
3.3 in and 5v tolerant

but +/- 5.5v out. For equipment that actually, meets the RS232 spec
is fine

> of level-converter would be required between it and the 232.
> Cheap, or you can make yer own, but it's an extra level of
> complication.
>
> Thing is, some of that old equipment (oft industrial) IS still
> out there doing its job so a Fake-to-Real RS232 (might add a
> couple other RS's) converter might be a worthwhile bit of kit
> to have around.
>
> There's also the issue of the flow-control lines. While modern
> stuff is fast enough to not worry about it, the old equipment
> might need to signal a brief stop while you are sending to it.
> Buffers were often very small back then (and processing slow).
>
> Async is versatile, but a pain in the rump sometimes. Synchronous
> serial is more civilized. However most equipment you'll ever come
> across is async.

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