5156Is there a Hex Keypad standard?
- Feb 1, 2007I built an Elf from the Popular Electronics 1976 article back in
1978 and around 1979 I added a hex key pad in place of the binary
interface (I used a solderless breadboard instead of the 8 switches
for cost reasons).
Click on the picture for a larger view.
My keypad is getting flakey and I'm thinking about a redesign and
thought that if there is a standard then I should adhere to that.
The following is a description of how my current keypad behaves.
My keypad drives the INPUT switch after every 2nd key press. This
also drives /EF4 and /DMA_IN low and drives 8-bit data onto the data
bus in response to the ELF doing a Port 4 read. I think the INPUT
to /EF4 and /DMA_IN and port 4 read is standard ELF behavior when
the machine is in the LOAD state.
I also have my keypad drive /EF3 low when any key is pressed
and /EF4 low when the LOAD button is pressed. I have a toggle
switch that selects between the LOAD button and the auto-load on
every 2nd key press.
This is my main user interface. Basically, I can look for EF3
active and then read port 4 to see which key is pressed under
program control or use the thing in auto-load mode to load programs
starting at location zero. The later is how I jump to my monitor
code that is held in ROM at location 0xf000.
The keypad also has 8 LEDs connected to PORT 4 as I could not afford
the HP hex displays back then.
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