C64/128 User Port

From HwB

Available at Commodore C64 & C128 computer. Can be used as RS232 port with software.



24 PIN MALE EDGE (DZM 12 DREH) at the computer.

Pin Name Description
1 GND Ground
2 +5V +5 VDC (100 mA max)
3 /RESET Reset, will force a Cold Start. Also a reset output for devices.
4 CNT1 Counter 1, from CIA #1
5 SP1 Serial Port 1, from CIA #1
6 CNT2 Counter 2, from CIA #2
7 SP2 Serial Port 2, from CIA #2
8 /PC2 Handshaking line, from CIA #2
9 ATN Serial Attention In
10 +9V AC +9 VAC (+ phase) (100 mA max)
11 +9V AC +9 VAC (- phase) (100 mA max)
12 GND Ground
A GND Ground
B /FLAG2 Flag 2
C PB0 Data 0
D PB1 Data 1
E PB2 Data 2
F PB3 Data 3
H PB4 Data 4
J PB5 Data 5
K PB6 Data 6
L PB7 Data 7
N GND Ground

Note: 0.156" (3.96mm) contact spacing.

The Commodore 64 gives you complete control over Port B on VIA chip #1. Eight lines for input or output are available, as well as 2 lines for handshaking with an outside device. The I/O lines for Port B are controlled by two locations. One is the port itself, and is located at 56577 ($DD01 hex). Naturally you PEEK it to read an input, or POKE it to set an output. Each of the eight I/O lines can be set up as either an input or an output by setting the data direction register properly. It is located at 56579 ($DD03 hex).