[Dclug] USB Serial Port Problem

[James Ewing Cottrell 3rd]

It all depends on what the device wants, but serial communication is 
typically 10 bits...one start bit (a space), 8 data (low bit first), and 
one stop bit (mark). Sounds like your first stop bit is being treated as 
the 8th bit and will be seen as a one. Most devices either want a 
specific parity (odd or even), but many will take space parity. Mark 
parity means that the device will specifically have to ignore the high 
bit. You may be feeding the device characters it doesn't know about, and 
it it is streaming them, you may get framing errors.

JIM

Two stop bits are used on 110 baud, but nowhere else that I know of.

One possibility is that you might want to do something like "sleep 99999 
< /dev/ttyxx" just to keep the device open. It's not clear that you 
aren't resetting it between characters, altho that's a longshot.

On 6/19/2010 4:21 PM, David C Niemi wrote:
> On Sat, 19 Jun 2010, Klosowski, Przemek wrote:
>
>    
>> It is possible that the Problem is that the port is too fast eg shooting
>> characters back to back instead one char at a time perhaps in the old
>> driver. I have seen simple serial ports getting confused by such fast
>> incoming data--i think they couldn't synch to start bit immediately
>> following a stop bit w/o mark space delay. To check this try outputing
>> one char at a time maybe even with few ms delay
>>      
> I'm only sending an occasional carriage return at 1200 baud, 7 bits, 2
> stop bits.
>
> Another change, I think, is that there is a second delay after every
> character sent, but it's possible that was always the case.
>
> +-----------------------------------------------------------+
> | David C Niemi  (Reston, VA, USA)  niemi at tuxers dot net |
> +-----------------------------------------------------------+
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