# C64/128 User Port

(at the computer)

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
M | PA2 | PA2
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).

Contributor: | Joakim Ögren, Nikolas Engström, Arwin Vosselman, Jestin Nesselroad, Larry Anderson

Source: | Commodore 64 Programmer's Reference Guide
| NT Rautanen Tietokonesivut: Commodore

Copyright © The Hardware Book Team 1996-2004.
May be copied and redistributed, partially or in whole, as appropriate.
Document last modified: 2002-01-13