Date : Wed, 06 Jan 1999 01:29:31 +0000
From : jgh@... (Jonathan Graham Harston)
Subject: Using PC keyboards
JGH wrote:
JGH> Does anybody know anything about using a PC keyboard with an Arc or
JGH> BBC?
Frank Lee <frank@...> wrote:
FL> For BBCs I seem to remember that the keyboard is just an array of
FL> switches across the (switched) data & address buses - keys connect
FL> specific pairs of lines & . PCs (and I think Arcs) have keyboards
FL> which generate t
/All/ keyboards are just an array of switches across the data and address
lines. Some keyboards carry these lines directly down the connecting
cable. On the BBC the connecting cable carries the 'address' and 'data'
lines as binary values. Ie, to test that the key at row 6, column 4 is
pressed, 6 is output to the row and 4 is output to the column. This, and
the resultant up/down bit read in. The connecting cable carries the
binary signal 01100100 which gets converted to the row addresser as
0000010000 and the column addresser as 0001000000.
The Arc and the PC keyboards contain a small processor which scans all the
rows and columns automatically, and on detecting a keypress or release
sends that information along the connecting cable in a serial format. So,
if the key at row 6, column 4 is pressed the keyboard /may/ send 0110 then
0100 in serial format to the computer (the exact values and data format
will be different to this explanation - that's exactly what I'm trying to
find out!)
When I experimented before I connected the Data line to the user port D7
input and the Clock line to the CB1 interupt input (plus 0v, 5v). I then
programmed the VIA to read serially from bit 7 on a transition of the CB
line. I then pressed and released keys. I got varying word lengths. I
couldn't work out a consistant way of getting the key information from the
bit-stream, and then I got bogged down in something else and didn't get
any further with it.
--
J.G.Harston (JGH BBC PD Library) 70 Camm Street, Walkley, SHEFFIELD S6 3TR
jgh@... --- BBC+Master / Z80+6502 / CoPro+Tubes / Econet+SJ
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