Signal Description of serial IEC bus ------------------------------------ Pin(s) Signal Dir Description 1 /SRQIN in/out Service request. This line is an input only at the C64's serial jack which connects to the /FLAG input of CIA #1. It was intended to be used by peripherals to request being served by the C64. The C128 uses this line for the fast serial transfer. 2 GND - Ground (0V). 3 /ATN in/out Attention. Set to low by the C64 to indicate the beginning of a serial data transfer. 4 /CLK in/out Clock. Used for software handshaking. 5 /DATA in/out Data! Check the warp drive! 6 /RESET in/out Reset. Input at serial bus jack of peripherals, output at C64's serial bus jacks. When pulled to LOW, resets every peripheral hooked up on the serial bus. In old C64 board versions, a serial reset also resets the C64. Author: Marc-Jano Knopp on 97/12/12 Source: http://mjk.c64.org