Signal Description of VIA 6522 ------------------------------ Pin(s) Signal Dir Description 1 GND - Ground (0V). 2-9 PA0-PA7 progr. Port A 0-7. Port A of the VIA #1 in the 1541 is not used so that you can connect a parallel cable here for speeding up floppy operations. Some modifications are needed for the 1541c and 1541-II, though. 10-17 PB0-PB7 progr. Port B 0-7. 18 CB 1 in/out Control port B 1. When configured as input, it can be used to trigger interrupts. 19 CB 2 in/out Control port B 2. When configured as input, it can be used to trigger interrupts. 20 Vcc - Supply voltage (+5V DC). 21 /IRQ out Interrupt ReQuest. In the 1541, this line is connected to the /IRQ input of the 6502. 22 R/-W in Read/-Write. 0=read on data bus, 1=write on data bus. 23 /CS 2 in Chip Select 2. CS2=0 AND CS1=1 = coupled to data bus, 1=tri-state. 24 CS 1 in Chip Select 1. In the 1541, this line is directly connected to +5V DC. 25 ø 2* in Phi 2. System clock signal. All data bus action takes place only when ø2=1. 26-33 DB7-DB0 in/out Data bus. 34 /RES in RESet. 0=reset the VIA to initial state. 35-38 RS3-RS0 in Register Select. These four pins select on of the VIA's internal registers. In the 1541, they are connected to A3-A0 of the address bus. 39 CA 2 in/out Control port A 2. 40 CA 1 in/out Control port A 1. * The 'ø' is used as Greek 'phi' here. progr. = programmable Author: Marc-Jano Knopp on 98/1/23 Source: http://mjk.c64.org/