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.
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.
The Details Explained
system functions are active-low Most of the functions in the PCE chart are active low
The descriptions for these pins are:
OE - Output Enable CDD - CD Detect (AKA K7, Input Bit 7) HuD - HuCard Detect HSM - High Speed Mode RST - Reset R/W - Read / Write /RDY - Ready IRQ2 - Interrupt 2 A20 is often used as CE - Chip Enable
CD Detect obviously isn't the correct term, as the Shuttle has it too and no CD peripheral was released for this unit, however it seems to be used for this purpose in normal PC Engines, so there you go. HuDetect indicates the presence of a HuCard in the slot (cart port pin 1 is low). Reset resets the machine (Surprise!) High Speed Mode either indicates or determines whether the system is running at full speed (7.2MHz)or low speed (1.8MHz). Interrupt Request 1&2 for... requesting ... interrupts. Shut up. Chip and Output Enable are both signals used with ROM chips to activate the device, and enable output respectively. Read/Write when set low the data bus is set to WRITE mode.
Power Vout - Voltage out. The PC Engine supplies +5v to peripherals from this port. Vin - Voltage in. You can power the PC Engine form this port. Note that power supplied through these pins bypasses the power switch, so the system will be ON regardless of switch position. Audio and video: SNDR and SNDL - Audio Right and Audio Left output. SNDin - Audio Input Video Bus (VD): HSn Horizontal Sync VSn Vertical Sync DCK Dot/Pixel Clock (5.36 / 7.16 / 10.73 MHz) VS Unknown VU Unknown VD1 - VD8 ViDeo Bus bits 1-8, directly connected to the video encoder (HuSomething) VD0-VD3 = four bit pixel value VD4-VD7 = four bit palette value VD8 = high for sprite/border pixels, low for background pixels (for genlock, or LaserActive use?)