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Tech and Homebrew => Turbo/PCE Game/Tool Development => Topic started by: TailChao on February 25, 2014, 05:20:24 AM

Title: Turbo Express / GT Com Port
Post by: TailChao on February 25, 2014, 05:20:24 AM

Hi all,

Before I start disassembling Bomberman, has anyone done any reverse engineering work on the Turbo Express / GT's COM port? I've checked the usual hardware documents and Mednafen's sources and neither has any info.

Title: Re: Turbo Express / GT Com Port
Post by: Arkhan on February 25, 2014, 07:10:57 AM

Quote from: TailChao on February 25, 2014, 05:20:24 AM

Hi all,

Before I start disassembling Bomberman, has anyone done any reverse engineering work on the Turbo Express / GT's COM port? I've checked the usual hardware documents and Mednafen's sources and neither has any info.

Talk to OldMan.  He was f*cking around with it at one point. 

Title: Re: Turbo Express / GT Com Port
Post by: TailChao on February 25, 2014, 08:43:10 AM

Quote from: Arkhan on February 25, 2014, 07:10:57 AM

Talk to OldMan.  He was f*cking around with it at one point. 

I got a message from him right as I saw your post :)
Thanks for the heads up though.

Title: Re: Turbo Express / GT Com Port
Post by: Arkhan on February 25, 2014, 09:11:34 AM

Quote from: TailChao on February 25, 2014, 08:43:10 AM

Quote from: Arkhan on February 25, 2014, 07:10:57 AM

Talk to OldMan.  He was f*cking around with it at one point. 

I got a message from him right as I saw your post :)
Thanks for the heads up though.

yeah, lol I recall that that was why I think I loaned him my express for awhile, to mess around with it.

Title: Re: Turbo Express / GT Com Port
Post by: TailChao on March 17, 2014, 02:56:58 AM

Good news:
I had time to do some reverse engineering last weekend.

Bad news:
Everything is bitbanged using CLR and SEL in the IO register :-&. The details are pasted below (taken from one of my equates files):

Code: [Select]

;****************************************************************
; Gamestick Joyport *
;****************************************************************
.define GAMESTICK_JOYPORT $1000
; -R/
; 7: CD-ROM Unit Attached
; 6: Nationality/Type (1 = PC-Engine, 0 = TurboGrafx)
; 5-4: '1'
; 3-0: Joypad Port D3-D0
; -/W
.define GAMESTICK_CLR %00000010
.define GAMESTICK_SEL %00000001
; 1: Joypad Port CLR
; 0: Joypad Port SEL

; The Turbo Express / PC Engine GT also uses this register for
; bitbanged data transfers over its COM port. This conveniently
; uses a 1/8" stereo cable connected as follows:
;
; Pin Register (W)
; ---- ---------
; Tip Bit 0 (SEL)
; Middle Bit 1 (CLR)
; Inside GND
;
; Setting CLR high (which also disables the joystick) enables
; reading the state of the COM port pins through $1000:
;
; Pin Register (R)
; ---- ---------
; Tip Bit 1 (CLR)
; Middle Bit 0 (SEL)
;
; For the most basic transfers, CLR can be a clock and SEL data.
I was hoping for some sort of UART to make PCE -> PC comms trivial like with the Lynx, but I guess I'll have to add that to a card.