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devel / comp.arch.embedded / Re: Linux embedded and direction control of RS485 transceiver

SubjectAuthor
* Re: Linux embedded and direction control of RS485 transceiverA.P.Richelieu
+- Re: Linux embedded and direction control of RS485 transceiverUwe Bonnes
`- Re: Linux embedded and direction control of RS485 transceiverpozz

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Re: Linux embedded and direction control of RS485 transceiver

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From: aprichel...@gmail.com (A.P.Richelieu)
Newsgroups: comp.arch.embedded
Subject: Re: Linux embedded and direction control of RS485 transceiver
Date: Sun, 9 May 2021 13:24:21 +0200
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 by: A.P.Richelieu - Sun, 9 May 2021 11:24 UTC

Den 2021-03-24 kl. 00:06, skrev pozz:
> I have an half-duplex RS485 bus with 10-20 different nodes. Some of them
> are 8-bit MCU based, one of them could be Linux embedded.
>
> It's half-duplex, so it's important for the transmitter node to disable
> the driver as soon as the last transmitted bit is shifted out.
>
> Many small low-cost MCU has interrupt on transmission complete, so the
> delay of disabling the driver is usually on the order of microseconds.
>
> Some new Cortex-M MCUs have an automatic control of external RS485
> transceiver, so the delay is really zero.
>
> What happens in Linux embedded systems? Many of them are based on NXP
> i.MX CPUs and it seems they aren't able to control the RS485 direction
> in hardware, but some code is needed. This approach could increase the
> delay of disabling the driver in the order of milliseconds.
>
> Is it possible that a powerful CPU isn't able to control RS485 driver in
> hardware?

Atmel (now Microchip) ARM products has a serial port which supports
handling the RS-485 direction in hardware. It also has an interrupt
which is triggered after a programmable delay has occured without any
receied characters.

Re: Linux embedded and direction control of RS485 transceiver

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From: bon...@hertz.ikp.physik.tu-darmstadt.de (Uwe Bonnes)
Newsgroups: comp.arch.embedded
Subject: Re: Linux embedded and direction control of RS485 transceiver
Date: 9 May 2021 12:01:02 GMT
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 by: Uwe Bonnes - Sun, 9 May 2021 12:01 UTC

A.P.Richelieu <aprichelieu@gmail.com> wrote:
> Atmel (now Microchip) ARM products has a serial port which supports
> handling the RS-485 direction in hardware. It also has an interrupt
> which is triggered after a programmable delay has occured without any
> receied characters.
>
Similar for recent STM32 U(s)arts.
--
Uwe Bonnes bon@elektron.ikp.physik.tu-darmstadt.de

Institut fuer Kernphysik Schlossgartenstrasse 9 64289 Darmstadt
--------- Tel. 06151 1623569 ------- Fax. 06151 1623305 ---------
(Phone also available during "mobile work")

Re: Linux embedded and direction control of RS485 transceiver

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From: pozzu...@gmail.com (pozz)
Newsgroups: comp.arch.embedded
Subject: Re: Linux embedded and direction control of RS485 transceiver
Date: Mon, 10 May 2021 09:46:15 +0200
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 by: pozz - Mon, 10 May 2021 07:46 UTC

Il 09/05/2021 13:24, A.P.Richelieu ha scritto:
> Den 2021-03-24 kl. 00:06, skrev pozz:
>> I have an half-duplex RS485 bus with 10-20 different nodes. Some of
>> them are 8-bit MCU based, one of them could be Linux embedded.
>>
>> It's half-duplex, so it's important for the transmitter node to
>> disable the driver as soon as the last transmitted bit is shifted out.
>>
>> Many small low-cost MCU has interrupt on transmission complete, so the
>> delay of disabling the driver is usually on the order of microseconds.
>>
>> Some new Cortex-M MCUs have an automatic control of external RS485
>> transceiver, so the delay is really zero.
>>
>> What happens in Linux embedded systems? Many of them are based on NXP
>> i.MX CPUs and it seems they aren't able to control the RS485 direction
>> in hardware, but some code is needed. This approach could increase the
>> delay of disabling the driver in the order of milliseconds.
>>
>> Is it possible that a powerful CPU isn't able to control RS485 driver
>> in hardware?
>
> Atmel (now Microchip) ARM products has a serial port which supports
> handling the RS-485 direction in hardware. It also has an interrupt
> which is triggered after a programmable delay has occured without any
> receied characters.

I know SAM D family MCUs has a nice SERCOM peripheral with RS485
direction in hardware.

But my discussion was for Linux embedded, so MPUs (Cortex-A).

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