[Coco] CoCo3 PIA?

[jdaggett at gate.net]

On 4 Jan 2007 at 16:23, Phill Harvey-Smith wrote:

> 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.

*********************

Phil

Both Port A and Port B  have weak pullups when configured as inputs. As I 
explained in my reply to Mark, an NMOS invertor does not a great deal of gate 
current to turn on. 50 nA is often more than sufficient. The load impedance from 
the driving source is often far less than this. 

james