4 Jun
2005
4 Jun
'05
2:30 p.m.
My Nascom is almost impossible to get to at the
moment, can you remind me
as to what chips are on the keyboard? I am going to guess at at least one
TTL decoder chip, and maybe not a lot else.
I've had a look at the NAS-SYS 3 source listing. I mamnaged to find the
keyboard scanning routine, and it would appear that the keyboard
incorporates a hardware scan counter. It's reset by one of the Q outputs
(Q1, I think) and incremented by one of the others (Q0?). The keyboard
row lines are read in on the bottom 7 of the D inputs. What the D7 input
is used for (shift???) and what the other 2 Q outputs do is something
I've not worked out yet.
-tony