|HuCard Pin||HuC6280 Pin||Name||Description|
|2||--||AUDIO_IN||Mono audio 2)|
|35||14||HSM||High Speed Mode: High=7.15909 Mhz, Low=1.7897725 Mhz|
|37||43||/IRQ2||Interrupt Request Line 2|
|38||--||VCC||+5 Volts DC|
- 1)When connected to ground, tells system there is a card inserted. TurboDUOs use this to know whether to run the internal CD System 3.0 card or to run the card connected to the HuCard port.
- 2)From what I can tell from circuit tracing, any signal fed into this pin gets mixed equally into the Left and Right audio channels before they are amplified and sent to the jacks. On the TurboDUO, the signal must be amplfied a bit for it to come out on the audio jacks, while on the TurboGrafx 16, it comes out much louder. I believe the DUO has some kind of register in the hardware that can turn this channel on/off so that it takes a much louder signal to get through the off state that it is in. I have not circuit traced a DUO to find out yet.
The TurboGrafx-16 differs from the PC Engine in that the D0-7 datalines are reversed (actually, the PROM is programmed that way, and the wires leading to the data bus in the machine are reversed). I have shown here, the card pinout (which does not differ). I believe that this is the PC Engine port pinout (TurboGrafx-16's just reverse the data lines' order; swap 0 for 7, 1 for 6, 2 for 5, and 3 for 4).
Additional information: to copy a TurboGrafx-16 game to work on a PC Engine with copier, reverse the bit order. There is then a sequence of code which checks what machine the game is running on: all known examples start with 78 54 A9, have the letters NEC at offset 15 hex, and an F0 at offset 0B. If the F0 is changed to an 80 (changing a conditional jump to an unconditional jump), the game will work on both PC Engine and TurboGrafx-16.
This code sequence is usually at the start of the game, but can be in other places.