Last Updated or created 2022-09-08
Divers new additions to the 6502 project
Above is my design for a hex keyboard to enter opcodes in hex using a simple monitor program.
i used a 74ls922 which can decode a 4×4 matrix. I’d rather had a 74ls723 which can encode 20 keys.
Nowhere to be found. So i have to think of a new plan.
Now it is configured as follows:
| C | D | E | F |
| 8 | 9 | A | B |
| 4 | 5 | 6 | 7 |
| 0 | 1 | 2 | 3 |
When pressing the alternate key
| addr (to implement) | run (1/2 implemented) | reset (to implement) | |
| step instruction (to implement) | |||
| memory next | |||
| memory previous |
Meanwhile i’ve ordered new keys (the ones i’ve been using for my photomanager project and wnat to have a setup like this:
| ? | ? | addr | run | reset |
| C | D | E | F | ? |
| 8 | 9 | A | B | step |
| 4 | 5 | 6 | 7 | mem next |
| 0 | 1 | 2 | 3 | mem prev |
When you want to show the status of busses and alike, you can’t use a led and restistor directly on the bus, it will require too much current.
So i’ve been using below schematic which uses a darlington array.
Now i can display databus, address bus and i’ve been using this for address decoding logic and hex keyboard.
I’ve implemented a second VIA chip, and ordered components to amplify the SID sound part