[Coco] CoCo3 PIA?

[Mark Marlette]

Phill,

I'll have to go back and re-read the data sheet.

I was looking for configurable pullups and not always preset pullups.

Get use to new technology and forget to look back. Configurable  
ullups, weak pullups on each pin.

Mark

Quoting Phill Harvey-Smith <afra at aurigae.demon.co.uk>:

> Mark Marlette wrote:
>> james,
>>
>> If the LSTTL is not being used as the pull up and the 68x21 doesn't
>> have configurable pullups. How does the circuit guarantee a hi level
>> for the CoCo3 keyboard interface?
>
> Port A which I believe is configured as inputs have internal pullups on
> all lines, which operate in either input or output mode. Since a keyrow
> with no keys pressed will not be connected to anything, the internal
> pullup should ensure the 1 level. A connected key on the row being read
> will of course be pulled down to zero, by dint of the output row being
> zero, which will overcome the pullup.
>
> This very behavior is used on a couple of the Dragons to pull up the rom
> select line of a rom, and ensure that it is selected at reset time.
>
> Cheers.
>
> Phill.
>
> --
> Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !
>
> "You can twist perceptions, but reality won't budge" -- Rush.
>
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