30 Mar
2011
30 Mar
'11
8:29 a.m.
On 3/30/11 2:06 AM, Rod Smallwood wrote:
I don?t know if this helps. I worked in VDU design
and development in the
mid 1970's. The keyboards used a system with a 74150 and I think a '154.
These are a 16 line binary to decimal decode and an eight line to binary
encoder. The outputs of the one and the inputs of the other formed a matrix
with the keys (switches) at the junctions. A counter drove the inputs of one
and the selects of the other. As soon as you got an output the counter
stopped and its value became the pressed key value.
Fairly standard matrix scanner..
-Dave
--
Dave McGuire
Port Charlotte, FL