Expansion Port

Extensions for the expansion port are quite numerous; Ramlink, SuperCPU, Final Cartridge, Action Replay, to name a few. In the old days, many game modules were available, too.
Note that devices connected to the expansion port (especially floppy speeders) are more incompatible than equivalent user port versions, as their ROM is mapped into the C-64 RAM.

Connection scheme

 
ASCII version:

 22 21 20 19 18 17 16 15 14 13 12 11 10  9  8  7  6  5  4  3  2  1
+==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==+
|                                                                 |
+==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==-==+
  Z  Y  X  W  V  U  T  S  R  P  N  M  L  K  J  H  F  E  D  C  B  A

Signal Description

Pin(s)	Signal	Dir	Description
1	GND	-	Ground (0V).
2-3	+5V	-	Supply voltage. Max. 450 mA.
4	/IRQ	in	Interrupt ReQuest. When going LOW, the CPU loads the PC with the value stored in $fffe/$ffff after processing the current command. This procedure will be executed only when interrupts have been enabled (bit 2 in flag register = 0). Note that the IRQ signal must be applied until the CPU has checked this pin; a short IRQ pulse is not sufficient [1].
5	R/-W	out	Read/-Write. During read cycles, this line is HIGH, and LOW otherwise. Note that all accesses only take place whenø2 is HIGH.
6	Dot Clock	out	VIC dot clock (PAL: 7.8MHz).
7	-(I/O1)	out	I/O #1. LOW, if an address between $de00 and $deff is on the address bus.
8	/GAME	in	This line can be used by an expansion port cartridge together with the /EXROM line to control the memory configuration. See below (Technical info) for details.
9	/EXROM	in	This line can be used by an expansion port cartridge together with the /GAME line to control the memory configuration. See below (Technical info) for details.
10	-(I/O2)	out	I/O #2. LOW, if an address between $df00 and $dfff is on the address bus.
11	/ROML	out	ROM High. LOW, if both an address between $df00 and $dfff is on the address bus and /EXROM is LOW.
12	BA	out	Bus Aavailable. If HIGH, the VIC-II uses the bus.
13	/DMA	in	Direct Memory Access. By pulling this line to LOW, the CPU will halt after the next read cycle and all bus connections will go to high-impedance state. This is useful for cartridges which replace the original CPU, like CMD's SuperCPU.
14-21	CD7-CD0	in / out	CPU Data bus.
22	GND	-	GrouND (0V).
A	GND	-	GrouND (0V).
B	/ROMH	out	ROM High. LOW if address $a000-bfff or $e000-ffff is on the address bus and the appropriate address range is banked out via /GAME and /EXROM.
C	/RESET	in	RESET. When going LOW, the CPU resets and waits for a LOW-HIGH transistion to load the PC with the value stored in $fffc/$fffd. After power-up, timer A in the NE556 pulls this line to LOW for a short time and half a second later back to HIGH.
D	/NMI	in	Non Maskable Interrupt. When going LOW, the CPU loads the PC with the value stored in $fffa / $fffb after processing the current command.
E	ø2 out*	out	Phi2 out. The CPU outputs the system clock for the rest of the chips for synchronization.
F-Y	CA15-CA0	in / out	CPU Address bus. The CPU applies the address of the next datum to be read or written.
Z	GND	-	GrouND (0V).

^* The 'ø' is used as Greek 'phi' here.

Technical info

 EXROM | GAME | Area redirected
 ------+------+----------------
  HIGH | HIGH | none (default)
  HIGH | LOW  | forbidden(?)
  LOW  | HIGH | $8000-9fff
  LOW  | LOW  | $8000-bfff

Note: All pictures show the plug side.

Site copyright © 1997 by Marc-Jano Knopp