I suppose I looked over these simple errors, and have now gotten
everything working perfectly, thanks everyone.

Jon

Mike Keitz wrote:
>
> On Sat, 16 Jan 1999 18:28:34 -0800 MARK D NEWPORT
> <jmnewp@worldnet.att.net> writes:
> >I finally tried to tackle this problem myself and am having some
> >difficulties.
>
> It would be helpful to us to describe exactly what the problems seem to
> be.  Looking at your code briefly, I see one minor problem and 2 major
> ones:
>
> A "comf PORTA,f" will do nothing to change the input value.  To invert
> the data, I'd complement the shiftreg variable after all the bits are
> shifted in.  But, you don't want to complement the received data.  If you
> use an inverting line reciever, zero data bits will read as low on the
> pin.  So the routine is OK as it is, just delete the comf.
>
> RS-232 data is transmitted LSB first.  Thus you need rotate *right* into
> the shift register, not left.  After 8 shifts, the LSB (which was
> received first) will be in its proper position.  [A common optimization
> is to initialize the shift register to 10000000, then test the flag after
> each rotate to see if the 1 came out.  When it does, 8 bits have been
> received.  This avoids the need for a bit counter variable.]
>
> Your routine returns immediately after taking the sample at the center of
> the last bit.  If you call it again right away (which you do) and the
> last bit transmitted was a zero, the routine will falsely detect the end
> of the last bit as a start bit, then go on to improperly receive a byte
> at the wrong time.  If the line was idle, the byte received will be all
> ones.  One work-around is to ensure there is a delay of at least 1/2 to
> 3/4 bit time (preferably 1 bit time, but not any longer) between calls to
> the receive routine to let the end of the last bit clear the line.  A
> probably better approach is to be sure the line is high (inactive, a stop
> bit) at the top of the routine, then start looking for a start bit.
>
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