Expansion Port

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[edit] Description

The Expansion Port of the C64

The Expansion Port, often called also Module, Cartridge or Memory Expansion Port. This port is a rectangular opening at the back of the C64 case and is intended for expansions of the system. Basically it corresponds with the ISA or PCI ports on a PC. Since all important signals of the C64 are led to the connector, this results in a wide range of applications. From just connecting a simple reset button a modem and EPROM programming device up to a SuperCPU there are almost all imaginable expansions possible. The expansion port is mainly used for plugging in cartridges which contain application software, games or additional RAM.

In opposition to the user port there are no free programmable lines at the expansion port, i.e. expansion port modules need to "listen" permanently to the data and address bus of the CPU MOS 6510 and influence the system with a conform timing. Therefore the expansion port is not suitable for simple projects.

[edit] Pin assignment

The expansion port is a 2-row EDGE connector with 44 contacts in total. The pitch of the contacts is 2.54 mm (0.1 inch).

Pin assignment


Pin Signal Meaning Remark
1 GND Ground (0 Volt)
2 +5V DCSupply voltage +5V DCThe maximum load for extensions is 450mA.
3 +5V DCSupply voltage +5V DCThe maximum load for extensions is 450mA.
4 /IRQInterrupt Requestsee IRQ
5 R-/WRead - /WriteHigh-level during read cycle, Low-level during write cycle
6 DOT ClkDot clock frequency7,88 MHz at PAL-systems ; 8,18 MHz at NTSC-systems
7 /I/O1Input/Output 1Low-level, if address bus within $DE00-$DEFF.
8 /GAMEGame configurationUsed for memory re-configuration; see PLA (C64-Chip)
9 /EXROMExternal ROMSimilar to /GAME. During low the internal RAM in the range of $8000-$9FFF will be switched off and /ROML will be set low, if one of these adresses occur.
10 /I/O2Input/Output 2Low-level, if address bus within $DF00-$DFFF.
11 /ROMLROM LowGets low, if the address range $8000-$9FFF is switched off with /EXROM and one of these addresses occur on the bus.
12 BABus AvailableSignal from the video controller, which indicates that the bus data are valid. If BA=1 the VIC allocates the bus and no other unit can use it.
13 /DMADirect Memory Accessif /DMA=Low the CPU can be requested to release the bus. It will stop after the next read cycle and all bus lines will go to high resistance state. So other units can use the computer hardware. At /DMA=High the CPU continues to work.
14 D7data line 7 data bus of the computer
15 D6data line 6
16 D5data line 5
17 D4data line 4
18 D3data line 3
19 D2data line 2
20 D1data line 1
21 D0data line 0
22 GNDGround(0 Volt)
A GNDGround(0 Volt)
B /ROMHROM HighDepending on the status of /GAME and /EXROM this line gets low during access to the address space between $A000-$BFFF respectively $E000-$FFFF. Condition: the internal ram area is faded out.
C /RESETResetIf this line will be pulled to low, all chips will be re-initialized. The program counter of the CPU will be loaded with the reset vector $FFFC and $FFFD (normally $FCE2).
D /NMINon Maskable Interruptsee NMI
E Ø2Phi 2system clock (0,98MHz at PAL, 1,02MHz at NTSC)
F A15address line 15 address bus of the computer
H A14address line 14
J A13address line 13
K A12address line 12
L A11address line 11
M A10address line 10
N A9address line 9
P A8address line 8
R A7address line 7
S A6address line 6
T A5address line 5
U A4address line 4
V A3address line 3
W A2address line 2
X A1address line 1
Y A0address line 0
Z GNDGround(0 Volt)

[edit] Links

Control Port · Expansion Port · User Port · Cassette Port · Power Supply Connector
A/V Jack · RF Jack · Serial Port


RS-232 · IEEE-488 · Centronics Interface
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