Commodore SX 64 I/O Board
- only two versions known (to me) 251106 Rev A and 251106 Rev 1, difference seems to be capacitor c9 that is missing in Rev 1.
- contains the logic and two CIA’s that the SX uses to communicate to external equipment like drives, printers and modems (and internal drive)
Integrated Circuits
| PCB Identifier | Chip Number | Remarks | Memory Location/bit |
|---|---|---|---|
| UC1 | 4066 | ||
| UB2 | 6526 | CIA 1 | $DC00-$DCFF |
| UB3 | 6526 | CIA 2 | $DD00-$DDFF |
| UD2 | 7406 | ||
| UE2 | 74LS74A | ||
| UE3 | 556 |
Schematics
Commodore SX 64 I/O Board Schematics 251107
Board Image
251106 REV A
251106 REV 1
interesting about the C9 on the rev 1
I just ran into that issue installing a switchless jiffydos board
I think c= directly soldered it to the 556 on that version
if you look at the 2 picks of UE3 v1 has a resistor soldered on as a afterthought and the other its on the board properly marked as C9
um my bad UE3 has a capacitor …not resistor
shouldn’t try and type before my morning coffee
Schematic lists:
UC1 should be 4066
UE2 should be 74LS74
UB2 should be 6526A CIA
UB3 should be 6526A CIA
UD2 should be 7406
UE2 should be 74LS74
UE3 should be 556
Actually the circuit list is all wrong….
Dear Michael,
Thank you for telling me,
I listed the parts list of the floppy disk controller card instead of the I/O card.
I fixed the error.
Regards,
Jeroen.