Pinout

Reference signals

Below are simple pictures of the different signals on the PLA MOS 906114-01 chip which I use for reference/comparison during fault finding. For further details about the signals on the different C64 custom chips I will highly recommend Sven´s techsite.

Settings on Philips/Fluke PM3055 60 MHz analog oscilloscope:

• 2 V / DIV

• See individual pictures for time settings

Signals have been measured on a working Commodore 64 assy 250466 in idle mode (blue screen).

Pin #1
N.C.

Pin #2
A13

Connected to A13 of the address bus

Pin #3
A14

Connected to A14 of the address bus

Pin #4
A15

Connected to A15 of the address bus

Pin #5
VA14

Connected to #VA14 on VIC-II

Used for programming field-programmable parts and not connected internally for mask programmable parts

Pin #6
CHAREN

Connected to #CHAREN on I/O port of the 6510 CPU

Pin #7
HIRAM

Connected to #HIRAM on I/O port of the 6510 CPU

Pin #8
LORAM

Connected to #LORAM on I/O port of the 6510 CPU

Pin #9
CAS

Connected to #CAS on the VIC-II

Pin #10
ROMH

#ROMH

Pin #11
ROML

#ROML

Pin #12
I/O

#I/O

Not so easy to see but the signal is pulled low for a very short period regularly.

Video capture of signal here

Pin #13
GR/W

GR/#W, connected to #WE on the color RAM

This signal is pulled low for a very short period regularly - quite the same way as pin #12.

Pin #14
VSS

Ground (GND)

Pin #15
CHARROM

Connected to #CS1 on the #CHARROM

Pin #16
KERNAL

Connected to #CS on the #KERNAL ROM

Pin #17
BASIC

Connected to #CS on the #BASIC ROM

Pin #18
CASRAM

Connected to the #CAS pin on the DRAM

Pin #19
CE

Chip Enable

Pin #20
VA12

Connected to VA12 on VIC-II

Pin #21
VA13

Connected to VA13 on VIC-II

Pin #22
GAME

Connected to #GAME on pin 8 of cartridge port

Pin #23
EXROM

Connected #EXROM on pin 9 of cartridge port

Pin #24
R/W

Connected to R/#W of the bus

Pin #25
AEC

#AEC, connected to inverted version of AEC on the VIC-II

Pin #26
BA

Connected to BA on the VIC-II

Pin #27
A12

Connected to A12 of the address bus

Pin #28
VCC

+5V

Banner picture credits: Xato