Interface Protocol of SEGA MegaDrive's 6-Button-Controller

Pin Assign (D-SUB9P)
# SignalName |   Explanation (Direction)
   ----------+---------------------------------
    1. D0    | Data         (Controller -> Mainframe)
    2. D1    | Data         (Controller -> Mainframe)
    3. D2    | Data         (Controller -> Mainframe)
    4. D3    | Data         (Controller -> Mainframe)
    5. +5V   | PowerSupply  (Supplied to Controller by Mainframe)
    6. D4    | Data         (Controller -> Mainframe)
    7. Sel   | SelectSignal (Mainframe -> Controller)
    8. GND   | Ground
    9. D5    | Data         (Controller -> Mainframe)

# All signals are TTL compatible.


In Case of 3-Button-Controller

 Sel  D0 D1 D2 D3 D4 D5
 Low  UP DW LO LO A  ST
 High UP DW LF RG B  C

   # LO --- Always Low
   # UP --- Up of Cross Key
   # DW --- Down of Cross Key
   # LF --- Left of Cross Key
   # RG --- Right of Cross Key
   # A ---- Trigger Button A
   # B ---- Trigger Button B
   # C ---- Trigger Button C
   # ST --- Start Button
   ## Low -> Pressed , High -> Not Pressed



Data Aquisition Sequence of 6-Button-Controller

Sel   D0 D1 D2 D3 D4 D5
Low   UP DW LO LO A  ST
High  UP DW LF RG B  C
Low   UP DW LO LO A  ST
High  UP DW LF RG B  C   # If there is two up-edge in 1.1 milli seconds,
Low   LO LO LO LO A  ST  # D0 - D3 go Low as Sel goes Low.
High  Z  Y  X  MD HI HI  # Make Sel High and read D0 - D3.
Low   HI HI HI HI A  ST  # Check that D0 - D3 go High as Sel goes Low.
High  UP DW LF RG B  C   # Once this sequence take place
Low   UP DW LO LO A  ST  # sequence can't be started for 1.8 milli seconds
.                        # after the first up-edge of Sel.
.                        # Only Datas read in 1.6 milli seconds from the
.                        # first up-edge of Sel are reliable.

   # LO --- Always Low
   # HI --- Always High
   # UP --- Up of Cross Key
   # DW --- Down of Cross Key
   # LF --- Left of Cross Key
   # RG --- Right of Cross Key
   # A ---- Trigger Button A
   # B ---- Trigger Button B
   # C ---- Trigger Button C
   # X ---- Trigger Button X
   # Y ---- Trigger Button Y
   # Z ---- Trigger Button Z
   # ST --- Start Button
   # MD --- Mode Button
   ## Low -> Pressed , High -> Not Pressed

Time parameters were measured by using my PC's timer.
It seems that the time is measured by discharging of
a capacitor in a 6-Button-Controller. It may mean
parameters differ one by one controller.
Please choose values you think proper for parameters.