C64 I/O Expansion Board
This is an expansion board I made for our son to use with the Commodore 64
to interface to his model railroad setup or whatever he wanted. Main I/O is
through two 26-pin headers. The DB-25 at the end is for a printer. The
board has two 6522's. Unfortunately, since the 6522 needs the CS lines
valid before its phase 2 goes up and the C64 doesn't meet that requirement,
I had to put in a circuit to delay the rising edge of phase 2 but not the
falling edge. Since the C64 lacks a reset button, I put one at the top
left. The LEDs are driven by buffers to show the status on VIA1PB without
loading it down.
Here's the wire-wrap side of the same board.
Since the issue of using the 6522 with a C64 has been raised before on the
forum, here's the notebook page on how that works.