Don L. Jackson wrote:
>
> At 08:51 AM 2/9/97 -0500, you wrote:
> >I hav been trying to get reliable serial communications on a 16C57 for
> >a while now, an almost have it working. The problem is that it doesnt
> >seem to get the first 3 bytes ok, they are always the same relative to
> >the data but wrong.
> >
> >Here is what I should receive:
> >
> > 36h 32h 30h 32h 30h 38h
> > The rest is ok.
> > This is what I get:
> >
> > 4dh 4ch 4ch 99h 98h 38h
> >
> >Can someone tell me whats wrong?
> >
> >Data rate is 2400 baud, Total bessage is 32 bytes, I only need the first
> >16.
> >
> >--
> >Alan Nickerson
>
> You may have a slight problem in timing, especially in processing each byte
> after it is received -- appears you may be missing a start bit or something.
>
> If you write out the bit pattern of what the data should be, least
> significant bit first from left to right on paper and insert a "10" between
> the bytes for the stop/start bits, and then a similar bit pattern of what
> data was received right below it, then you'll see that you are receiving
> the data bits but out of frame sync.  (Whew! what a sentence!)  The
> resultant data patterns will be skewed from each other.
>
> What algorithm are you using?
>
I am polling the receive pin 3 consecutive times, if each test shows the
start bit
then I call the receive buffer function.

Here is a little more of the operation.

The remote device sends an '>' (E3h) every 1.5 - 2 seconds. After that I
can send
a command. The receiving of the E3h works fine. After I receive the E3h
and respond
with my command, (in this case a request status). The remote system
sends it's
status message, however the first 3-5 bytes are mangled but the rest is
fine.

I cannot use an external clock to generate an interrrupt because the
hardware
design is already in use. I also cannot make any modifications to the
current
electronic design. A simmilar function is already in use with a
different remote
device, and this would be an upgrade to the newer remote unit.

Thanks for your help.

--
Alan Nickerson
---------
It seems to me that the best new ideas come from
people who don't know that they "can't".  -- Paul Mathews,
optoeng@WHIDBEY.COM