Re: [PATCH] Documentation about RS485 serial communications

[Grant Edwards]

On 2010-11-16, Alan Cox <alan@xxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, 16 Nov 2010 10:13:22 -0600
> Matt Schulte <matts@xxxxxxxxxxxxxxxxxxxx> wrote:
>
>> On Tue, Nov 16, 2010 at 8:30 AM, Pavel Machek <pavel@xxxxxx> wrote:
>> > Hi!
>> >
>> >> Documentation about RS485 serial communications
>> >
>> > I have seen hardware (kontron pmc-6l) that was capable of switching
>> > between RS232, RS485 and one other standard by software.
>> >
>> > Is such hw common? If so, should we have standard interface?
>> 
>> In my opinion this type of card is not that common.  Generally
>> speaking the achievable baud rates for this type of multi-protocol
>> card are very limited because of limitations of the transceiver chips.
>>  It seems that most of the time people would rather have a faster
>> serial port than one that does several different voltages
>
> If there are two types in common use then thats enough to say we should
> have a common interface IMHO

Comtrol, Moxa, B&B, Sealevel, and others all sell PCI cards and
Ethernet attached serial ports that have selectable interfaces
(typically RS-232/422/485).  Comtrol and Moxa have had drivers in the
kernel tree for ages, but they've always had to use custom ioctl calls
for things like configuring 232/485/422 mode and half/full-duplex
mode.

There are also tons of small Linux-based industrial server appliances
from Comtrol, Silex, Digi, Moxa, and others that have selectable
interface serial ports.

Having a standard API for things like interface mode, half-full
duplex, inter-character timeout, 9-bit mode, and so on would be life a
lot easier for those of us who maintain Linux serial drivers...

-- 
Grant Edwards               grant.b.edwards        Yow! I always have fun
                                  at               because I'm out of my
                              gmail.com            mind!!!

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