Re: Serial Communication Problem

"Scott McPhillips [MVP]" <org-dot-mvps-at-scottmcp>
Fri, 9 May 2008 10:42:19 -0400
"Marius" <> wrote in message

I suspected that the driver is, for some reason, not forwarding my
application the incoming data. So, to find out a little bit more, I ran a
"serial analyzer" tool to see if the scanner is actually sending any data.
In this software, I did a "New Serial Terminal Session" and I specified
COM 3 with 9600, 8, N, 1, Flow Control: None. I started this session,
scanned a barcode and data was displayed so I concluded that the scanner
is sending the data and closed this analyzer tool.

After that, I ran my application (without modifying anything in its source
code) and scanned a barcode and indeed, this time the event got signaled
and the data was correctly captured.

I re-booted my machine, started my application again, scanned a barcode
and it did not receive it. I ran the analyzer tool again, did the same
thing as before, closed it and then ran my application. Again, my
application received the data successfully. Therefore, I concluded that
somehow I am not initializing the communication correctly but I have no
idea what to do.

Are you calling SetCommState? Make sure you do that and review all of the
settings it controls. To learn more, you might want to call GetCommState
after your serial analyzer has "fixed" the problem. This will show you what
settings it set.

Are you calling SetCommTimeouts? This controls the conditions that will
cause WaitForSingleObject to return. The basic idea is that you should set
the timeouts so WaitForSingleObject will return if a number of milliseconds
elapse with no new input arriving.

Scott McPhillips [VC++ MVP]

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