Unfortunately I need the pins to behave much like a pin on a=20
traditional PIC.. that is, being able to be individually driven high or=20
low or read as an input.

Basically I have weak pullups/pulldowns on everything - and then I set=20
everything to a weak high pullup then pull one pin low and see which=20
other pins went with it.  Then do the same for a pulldown, except I pull=20
one pin high.   Repeat for each of the 128 pins...

I think I'm just going to try this with the eight I need for this design=20
and see how it works.  I realized I actually have two SPI devices on=20
this pic so perhaps I'll be ok...

-forrest

On 9/12/10 7:10 AM, Isaac Marino Bavaresco wrote:
>   Em 11/9/2010 22:36, Forrest W Christian escreveu:
>>    I am building a test apparatus (ok, it's a cable mapper) which will
>> require around 256 bits of I/O on a pic system.  Maybe even more.
>>
> If you don't need the pins to be bi-directional you could use the
> 74HC595 (output only) and 74HC597 (input only). They work serially and
> can be daisy-chained, you would save all the chip-selects.
>
> Isaac
>
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