The HuCard (marketed as TurboChip in North America) is a credit-card-sized ROM cartridge format developed jointly by NEC and Hudson Soft for the PC Engine game console, introduced in Japan on 30 October 1987 and subsequently used on the North American TurboGrafx-16 from 1989. The card connects via a proprietary 38-pin PCB edge connector driven directly by the HuC6280 CPU, which presents a 21-bit post-MMU physical address bus (PA0–PA20) and an 8-bit bidirectional data bus (D0–D7) on a single +5 V supply. Maximum addressable ROM capacity via the 21-bit bus is 2 MB (16 Mbit), though most commercial titles used 512 KB–1 MB; the Street Fighter II Champion Edition HuCard employed a 2.5 MB ROM with an on-card mapper. The PC Engine and TurboGrafx-16 share the identical 38-pin connector, but the TG16 mainboard wires the data lines in reverse order (D7…D0 on pins 15–23 rather than D0…D7), providing de-facto regional lockout.
| Pin | Name | Description |
|---|---|---|
| 1 | ? | |
| 2 | ? | |
| 3 | A18? | Address 18 |
| 4 | A16 | Address 16 |
| 5 | A15 | Address 15 |
| 6 | A12 | Address 12 |
| 7 | A7 | Address 7 |
| 8 | A6 | Address 6 |
| 9 | A5 | Address 5 |
| 10 | A4 | Address 4 |
| 11 | A3 | Address 3 |
| 12 | A2 | Address 2 |
| 13 | A1 | Address 1 |
| 14 | A0 | Address 0 |
| 15 | D0 | Data 0 |
| 16 | D1 | Data 1 |
| 17 | D2 | Data 2 |
| 18 | GND | Ground |
| 19 | D3 | Data 3 |
| 20 | D4 | Data 4 |
| 21 | D5 | Data 5 |
| 22 | D6 | Data 6 |
| 23 | D7 | Data 7 |
| 24 | /CE | Chip Select |
| 25 | A10 | Address 10 |
| 26 | /OE | Output Enable |
| 27 | A11 | Address 11 |
| 28 | A9 | Address 9 |
| 29 | A8 | Address 8 |
| 30 | A13 | Address 13 |
| 31 | A14 | Address 14 |
| 32 | A17 | Address 17 |
| 33 | A19? | Address 19 |
| 34 | R/W | Read/Write |
| 35 | ? | |
| 36 | ? | |
| 37 | ? | |
| 38 | +5V | +5 VDC |
Notes
- Pin 1 is the short pin on the left (if the card is to inserted forwards)
- Pin 38 is the long pin on the right
- Pin 1 (/CD — card detect) is pulled to GND inside every HuCard; this signals card presence to the console and to the CD-ROM2 subsystem. On the PC Engine expansion port it is labelled /CARD.
- Pin 2 (AUDIO IN) carries a mono analogue audio signal from the cartridge that the console mixes equally into both stereo output channels, allowing ROM cards to supply additional audio.
- Pin 24 (/CE, shown as Chip Select) corresponds to CPU address line PA20, which also functions as the active-low chip-enable for the ROM.
- Pin 26 (/OE) is the CPU read strobe (/RD) — an input to the cartridge asserted by the CPU during read cycles.
- Pin 34 (R/W) is the CPU write strobe (/WR) — an input to the cartridge asserted by the CPU during write cycles.
- Pin 35 (HSM — High Speed Mode) is driven by the CPU: asserted HIGH when the CPU runs at 7.15909 MHz, de-asserted at 1.7897725 MHz (÷4). Cartridges may monitor this signal to adjust ROM access-time requirements.
- Pin 36 (/RST) is the active-low reset input to the cartridge.
- Pin 37 (/IRQ2) is the only interrupt output line from the cartridge to the CPU; it is level-triggered and shared with the expansion port.
- Address lines PA0–PA19 appear in a non-sequential order across pins 3–14 and 25–33, matching standard 1-Mbit EPROM footprints. The full 21-bit physical address bus is managed by eight MPR mapping registers inside the HuC6280, each mapping an 8 KB logical window over up to 2 MB of physical space.
- The TurboGrafx-16 uses the same 38-pin connector, but wires D0–D7 in reverse order (D7 on pin 15 through D0 on pin 23) via reversed PCB traces from the cartridge slot to the CPU; HuCards for each region are ROM-programmed accordingly.
Signals
- /CD — Card detect; pulled to GND by the HuCard, signalling insertion to the console and the CD-ROM2 subsystem (pin 1)
- AUDIO IN — Mono analogue audio input from the cartridge, mixed equally into both stereo output channels by the console (pin 2)
- A0–A19 — Post-MMU CPU address lines PA0–PA19, routed in non-sequential order across pins 3–14 and 25–33
- D0–D7 — 8-bit bidirectional data bus; on the PC Engine, D0 is on pin 15 ascending to D7 on pin 23
- /CE — Active-low chip-enable for the ROM; this line also carries CPU address line PA20 (pin 24)
- /OE — Active-low read strobe from the CPU, asserted during read cycles (pin 26)
- R/W — Write strobe from the CPU, asserted during write cycles (pin 34)
- HSM — High Speed Mode; driven HIGH by the CPU at 7.15909 MHz, LOW at 1.7897725 MHz (pin 35)
- /RST — Active-low reset input from the console (pin 36)
- /IRQ2 — Active-low interrupt request output from the cartridge to the CPU (pin 37)
- GND — Ground reference (pin 18)
- +5V — Single +5 V supply to the cartridge (pin 38)