Expansion Port

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The PC Engine Expansion Port

The PC Engine expansion includes pins for just about everything, including the entire cartridge port, RGB, audio, video and a few other things. It also has access to the communications between the video chip and the CPU.

    Power    Audio/Video    Data Bus    Address Bus    System Functions    Video Bus (?)

The PC Shuttle Expansion Port

The PC Engine Shuttle had a cut-down expansion connector. The primary change is the removal of the video bus pins and the IRQ2 pin, preventing the Shuttle from using a CD ROM peripheral.

    Power    Data Bus    Address Bus    System Functions

Label Explanations

Most of the functions in the PCE chart are active low.

System Functions

OE Output Enable Chip and Output Enable are both signals used with ROM chips to activate the device, and enable output respectively.
CDD CD Detect (aka K7 and Input Bit 7) Used for detecting the presence of a CD expansion unit
HuD HuCard Detect Indicates the presence of a HuCard in the slot (cart port pin 1 is low)
HSM High Speed Mode Indicates or determines whether the system is running at full speed (7.15909 MHz)or low speed (1.7897725 MHz).
RST Reset Reset resets the machine
R/W Read / Write When set low the data bus is set to WRITE mode.
/RDY Ready
IRQ2 Interrupt 2 Used to trigger events in the HuC6270
A20 is often used as CE Chip Enable Chip and Output Enable are both signals used with ROM chips to activate the device, and enable output respectively.

NOTE: All system functions are active-low. If incorrect, please correct the wiki.


Vout Voltage out +5v power supply for peripherals connected to the expansion port.
Vin Voltage in Sends power directly to the PC Engine, bypassing the power switch.


SNDR Sound Right The right audio channel.
SNDL Sound Left The left audio channel.
SNDin Sound Input Single channel audio input.

Video Bus

HSn Horizontal Sync
VSn Vertical Sync
PCC Pixel Clock Possible values: 5.3693175 / 7.15909 / 10.738635 MHz
VS Unknown
VU Unknown
VD0 - VD3 Video Bus lines 0 - 3 four bit pixel value
VD4 - VD7 Video Bus lines 4 - 7 four bit palette value
VD8 Video Bus line 8 high for sprite/border pixels, low for background pixels

NOTE: VD0 - VD8 are directly connected to the HuC6260 VCE

Information gathered from GameSX.com