[TI-H] Re: PIC Interfacing - Web page update(hardware ?)

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[TI-H] Re: PIC Interfacing - Web page update(hardware ?)


Sami,
	Could you explain why you need the 18K ohm resistors on the
serial lines???  I see that VDD is on the other node but I don't
understand why the serial lines cannot be directly connected???  Also
what is the purpose of the Diode that is on RA3?  Sorry to sound so dumb
but I'm still kinda learning and I would really appreciate any feedback
you could provide.

Thanks,
Cullen Logan

-----Original Message-----
From: ti-hardware-bounce@lists.ticalc.org
[mailto:ti-hardware-bounce@lists.ticalc.org] On Behalf Of Sami Khawam
Sent: Friday, November 23, 2001 6:42 PM
To: ti-hardware@lists.ticalc.org
Subject: [TI-H] Re: PIC Interfacing - Web page update(hardware ?)


Hi,

It is possible to use only one pin per line - on the PIC you
either put the line in input mode (to get the high-Z state)
or you put it in output mode with zero out (to get the 0 state).

This is what I did in the PIXpander (using a PIC16F84). Check
the schematic and asm code on my page.

Regards,

Sami Khawam
http://sami.ticalc.org




Carlos Becker wrote:
> 
> At 17:42 23/11/2001 -0600, you wrote:
> 
> >OK,
> >         On your schematic you have each calc serial channel tied to
two
> >separate pins on the IC.  Is this really necessary?  If both channels
> >are bidirectional and each pin on the chip is bidirectional then why
do
> >you need to use two pins per channel.  From what I understood the
pins
> >on the PIC can be input or ouput.  If this isn't so then I understand
> >the need for it, please correct me if I am wrong.  These PICS are
very
> >particular.
> 
> You're right, pins are bidirectional. To change from input to output
you
> have to change the trisa / trisb registers. It was the first approach
I
> made, and after trying for about two weeks I thought of changing to
two
> inputs and two outputs and it worked. So, in conclusion, it didn't
work
> with only two pins. I tried pullups, pull- downs (if they're called
like
> that) and everything I could think of. But it didn't work, and
curiously it
> did when I changed to two outputs and two inputs.. strange.
> The software (pic program & ti-92+ program) were the same in both
cases, so
> it's even more strange. (well, the pic code was changed to fit to two
or
> four pins, just that).
> 
> You could try it, it's just question of typing some code. If you make
it,
> let me know.
> 
> Cya
> 
> Carlos Becker
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