17 Mar
2007
17 Mar
'07
4:24 p.m.
I think the keyboards were made up by putting keyswitches into a metal
plate then wiring them up in row and column form. A ttl system scanned
the rows and columns until it found a closed switch. The count was then
equal to the value of the character.
Almost certainly it was, it's how just abotu all keyboards of the period
worked. Before ROM became cheap enough to use to re-map the keyboard
matrix, it was common to wire the matrix so that the physical postiion of
the swtich related to the ASCII code (if you concatenate the row and
column binaray numbers, you end up with something like the ASCII code of
the character). Later on, ROM was cheap enough that it made more sense to
wire up the matrix in the most convenient from the point of view of
routing the tracks (adjacent keys were then in the same row or column of
the electrical matrix), and to use a ROM to convert the concatenated row
and column numbers to the ASCII code.
Howevery, you're missing my point. The Newbury terminal I have has the
keyboard in a separate case. It links up with a fairly wide ribbon cable,
and IIRC there are no chips in the keyboard. The encoder circuitry is in
the main part of the terminal (and probably does work as you've
described, I don't have schematics to check, and I've not got round to
tracing them out...)
-----Original Message-----
[...]
I have a Newbury terminal somwehre. I forget the model, but it's a later
one with a separate keyboard linked up by a wide ribbon cable (I think
the connections are just the row and column lines of a switch matrix,
there's not much, if any, electronics in the keyboard).
Now do you see what top-posting is a right pain in the rear?
-tony