Date   : Wed, 31 Aug 1994 13:09:38 +0100
From   : jfid@... (James Fidell)
Subject: Re: Keyboard & T1 interaction

lamcw wrote:

> 
> Bonfield James wrote:
> 
> ;Now I've got another question about the keyboard. Do only keypresses
> ;generate interrupts? It seems that the T1 interrupt checks the
> ;keyboard map again. I haven't scanned this carefully yet, but it
> ;seems probable that it's searching for key releases and updating
> ;&EC/&ED accordingly. My current implementation generates interrupts
> ;upon both press and release. However it's not working either.
> ;Although I think this problem is more due to the interaction between
> ;T1 and the KEYV. Somehow T1 isn't using the fact that KEYV has
> ;spotted a key press.
>
> i didn't think an interrupt was generated upon release of a key but it
> is an interesting point. at the mo, i'm only doing an int when a key
> is pressed.

Judging from the circuit diagram of the keyboard, CA2 is only pulled
low when a key is pressed.  The system VIA only generates interrupts
when CA2 goes low, so there's no need to generate an interrupt when
a key is released.

> ;I simply can't believe how long it's taking me to get this keyboard
> ;IO working.
>
> yes, frankly it's tougher than the CRTC and ULA. it's so poorly
> documented.

What do you mean -- there's all the documentation you could possibly
need.  Unfortunately, it's all written in 6502 assembler :-)

James.

-- 
 "Yield to temptation --             |
  it may not pass your way again"    |     jfid@...        
                                     |
        - Lazarus Long               |              James Fidell