I decided to finally let this little piece of information go out to the list.
The first complete HuCard pinout!
HuCard Port (For a TurboGrafx 16)
HuCard HuC6280 Signal Name Function Description
Pin # Pin#
1 -- /CARD_DETECT 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 -- AUDIO_IN 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.
3 65 A19 Address 19
4 68 A16 Address 16
5 69 A15 Address 15
6 72 A12 Address 12
7 79 A7 Address 7
8 80 A6 Address 6
9 1 A5 Address 5
10 2 A4 Address 4
11 3 A3 Address 3
12 4 A2 Address 2
13 5 A1 Address 1
14 6 A0 Address 0
15 56 D7 Data 7
16 55 D6 Data 6
17 54 D5 Data 5
18 -- GND Ground
19 53 D4 Data 4
20 52 D3 Data 3
21 51 D2 Data 2
22 50 D1 Data 1
23 49 D0 Data 0
24 64 A20 Address 20
25 74 A10 Address 10
26 62 /RD Read Strobe
27 73 A11 Address 11
28 77 A9 Address 9
29 78 A8 Address 8
30 71 A13 Address 13
31 70 A14 Address 14
32 67 A17 Address 17
33 66 A18 Address 18
34 63 /WR Write Strobe
35 14 HSM High Speed Mode: High=7.15909 Mhz,
Low=1.7897725 Mhz
36 11 /RESET System reset
37 43 /IRQ2 Interrupt Request Line 2
38 -- VCC +5 Volts DC