14207RCA VIP keypad
- Jul 1, 2013Hi,
The manual for the VIP doesn't go into the details of the ROM monitor. I am curious how the keypad functions. It uses a 4515 4-line to 16-line decoder, the inputs are D0-D3, the outputs are connected to the individual hexadecimal switches, the common end of all switches are wired to EF3.
So I suspect that when run, the VIP polls each switch in a loop (0-15), and addresses the 4515, places the relevant nibble on the data bus to enable the key output, and if the key is found pressed - EF3 goes high which would then trigger a branch operation to handle the key press.
Does this sound correct? Thanks.
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