IO Support Header Values

For anything related to IO (joypad, serial, XE...)

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Mask of Destiny
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IO Support Header Values

Post by Mask of Destiny » Wed Jan 10, 2018 8:03 am

I was wondering what values were legal for the IO support field in the standard Sega ROM header so I poked around a bit. This page from the official docs gives quite a few of them, but omits newer peripherals. Looking at the games in my collection I was able to fill in a few gaps and come up with the following list
  • J = 3-button gamepad
  • O = 2-button SMS/Mark III pad
  • 6 = 6-button gamepad
  • 4 = Sega Team Player (Note games that only support the EA 4-Way Play tap don't seem to indicate that in this header at all)
  • K = 10 Key Pad
  • R = RS-232C device (basically the modem)
  • P = Printer
  • T = Tablet (unreleased)
  • M = Mouse
  • B = Trackball (essentially an alias for the mouse, Nobunaga's Ambition uses this)
  • V = Paddle Controller (unsure if this is the Mark III paddle controller or an unreleased MD peripheral)
  • F = Floppy Drive (unreleased)
  • C = CD-ROM Drive (i.e. Mega CD)
  • A = XE-1AP
  • L = Activator
Game Toshokan uses 'JDR' in this field, but it's unclear what the D means. The only other place I've seen D is in SGDK projects (not sure why).

Menacer games don't appear to have anything other than J in the IO support field (at least the ones I own do not anyway).

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Re: IO Support Header Values

Post by Sik » Wed Jan 10, 2018 10:57 am ... doc/header

Code: Select all

   ID  | Device                ID  | Device
   ----+--------------------   ----+----------------------
   "A" | Analog joystick       "M" | Mouse
   "B" | Trackball             "P" | Printer
   "C" | CD-ROM (Mega CD)      "R" | RS-232 device (modem)
   "D" | ???                   "T" | Tablet
   "F" | Floppy drive          "V" | Paddle controller
   "G" | Lightgun (Menacer)    "0" | SMS controller
   "J" | 3 button controller   "3" | ???
   "K" | Keyboard or keypad    "4" | 4-way multitap
   "L" | Activator             "6" | 6 button controller
"3" seems to be a misunderstanding from a developer and actually means the same as "J". Meanwhile "D" is a mistery (Sega Game Library has it so you'd think it stands for "download"... but Rambo III includes it too which is WTF worthy)

Also many games have pure garbage here, so don't trust this field too much.

EDIT: also on M and B, they aren't necessarily aliases. Sure, the Sega Mouse (not Mega Mouse) acts as both, but games normally support only one of the two modes, which is what the header is referring to. Also the distinction was done early on (before the mouse was released), so it's likely that it was originally intended to be a discrete trackball.
Sik is pronounced as "seek", not as "sick".

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