I think you need the pullup resistors at least, as these prodive the type
of output that you need. Without them you essentially short the pins of
the PIC when the calc is low and you set a pin high on the pic. (Or vice
verso) At least that's what I think, I could be wrong though.

___________________________________________
Wesley Moore
RMIT - BEng/BApp.Sc. 2nd Year

wmoore@cs.rmit.edu.au
http://wmoore.tsx.org/

On Thu, 27 Apr 2000, Andrew Seddon wrote:

> Sorry for the large post but I have no website.
>
> Well there`s good news and bad news. First off I have kind of got the
> interface routines working. I say that because it sometimes works and
> sometimes dosn`t. When I program my TI-83+ to read a byte then spew it back
> out everything works fine. However when I try to make two TI`s, a 83+ and a
> TI-82 talk through the PIC it dosn`t work!! Dammned if I know whats up..
> Below is the code that I am using if anybody is interested or can find a bug
> in it.
>
> BTW it`s in C2C but most of the custom function calls are self explanitary.
> Sorry about the lack of comment.
>
> The calc variable is used as I have two calculators connected to one PIC,
> both operating off the lower four bits of the A and B ports. The electrical
> connection is just
>
> CALC 1 - WHITE - A0 + A2
>         - RED   - A1 + A3
>
> CALC 2 - WHITE - B0 + B0
>         - RED   - B1 + B3
>
> there are no resistors, diodes anyting, is that the problem??
>
> Here`s the code. Some redundent code commented out, was used it testing.