Expansion Port

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.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16	17	18	19	20	21	22	23
C	SNDR	GND	HuD	CEK	A17	A13	A11	GND	D2	D4	D6	D7	A1	A3	A4	A6	GND	A15	A19	GND	Vout	Sync	Blu
B	SNDin	CDD	HSM	/WR	VU	A8	/OE	D0	D3	D5	HSn	A0	A2	VD6	A5	A7	A12	A16	A20	/RDY	IRQ2	/RST	Grn
A	SNDL	Vout	VS	A18	A14	A9	A10	D1	PCC	VSn	Vin	VD8	VD7	Vin	VD5	VD4	VD3	VD2	VD1	VD0	GND	Vid	Red
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.

	1	2	3	4	5	6	7	8	9	10	11	12	13	14	15	16
C	GND	Vout	A07	A04	A01	GND	D2	D5	GND	A10	A08	A17	GND	/OE	CDD	GND
B	GND	Vout	A12	A05	A02	GND	D1	D4	D7	A20	A09	A14	GND	HSM	Vout	GND
A	A19	A16	A15	A06	A03	A00	D0	D3	D6	GND	A11	A13	A18	/WR	Vout	/RST
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.

Power

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.

Audio

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