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[LASERDISC] What CPU is this? what machine language instruction set does it use?
#382969 - 07/03/19 06:13 AM
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Hey all,
I am currently in the process of dumping all of my arcade laserdiscs using the Domesday Duplicator and a calibrated LD-V4300D (thanks to Simon Inns!). Results are very good so far but one problem is dumping Dragon's Lair 2 which has stop codes. The laserdisc player, by default, will pause the disc when encountering the stop codes which isn't going to work.
So I thought it wouldn't be too hard (ha ha ha!!) to just modify the EPROM and disable the part that pauses on stop codes.
I got the ROM dumped (it's a standard 27C256), but when it came time to identify the CPU, it appears to be a possibly proprietary CPU from Pioneer labeled 'PD0081B1'. I am kinda blocked at this point. Does anyone know anyone about this IC? I am hoping that it uses another CPU's instruction set. I saw some address vectors at the end of the ROM that look like what the 6502 and 6809 do.
I am not totally sure that this is the CPU, but from looking at the schematics, it is the most likely candidate since it has both address and data lines.
https://photos.app.goo.gl/fxsuctvrSnkz7b9C7
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: Matt Ownby]
#382970 - 07/03/19 10:53 AM
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I'd guess it's a Mitsubishi CPU, possibly with an internal program ROM. There are a bunch of them that we don't emulate.
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: Vas Crabb]
#382971 - 07/03/19 02:17 PM
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Pinouts appear to match several members of the Mitsubishi MELPS 740 series, which runs a variation of the 6502 instruction set. MAME already has some support for the MELPS 740.
The "CONT" board schematics actually show two of these, labeled "MECHA CONTROL" and "MODE CONTROL." The CNVss pin appears to pulled up for the former, making it execute from the 27C256, and pulled down for the latter, which must execute from internal ROM instead.
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: AJR Hacker]
#382973 - 07/03/19 06:55 PM
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> Pinouts appear to match several members of the Mitsubishi MELPS 740 series, which
> runs a variation of the 6502 instruction set. MAME already has some support for the
> MELPS 740.
>
> The "CONT" board schematics actually show two of these, labeled "MECHA CONTROL" and
> "MODE CONTROL." The CNVss pin appears to pulled up for the former, making it execute
> from the 27C256, and pulled down for the latter, which must execute from internal ROM
> instead.
Good call. I initially thought this was x86 machine language, but I tried disassembling it as if it was MELPS 740 and got something that looked pretty sane:
Code:
ROM:B1DF RESET:
ROM:B1DF sei
ROM:B1E0 clt
ROM:B1E1 cld
ROM:B1E2 clc
ROM:B1E3 clv
ROM:B1E4 clb 4, $FF
ROM:B1E6 ldx #$BF
ROM:B1E8 txs
ROM:B1E9 ldm #$FF, $E8
ROM:B1EC ldm #$20, $E9 ; ' '
ROM:B1EF ldm #$FF, $EA
ROM:B1F2 ldm #$28, $EB ; '('
ROM:B1F5 ldm #$FF, $EE
ROM:B1F8 ldm #3, $ED
ROM:B1FB lda #$C7
ROM:B1FD sta $4000
ROM:B200 lda #$FE
ROM:B202 sta $4001
ROM:B205 lda #$ED
ROM:B207 sta $4002
ROM:B20A lda #$AF
ROM:B20C sta $4003
ROM:B20F lda #$FA
ROM:B211 sta $4004
ROM:B214 lda #$50 ; 'P'
ROM:B216 sta $4006
ROM:B219 lda #0
ROM:B21B sta $4007
ROM:B21E lda #$7F
ROM:B220 sta $6000
ROM:B223 lda #$FF
ROM:B225 sta $6001
ROM:B228 lda #$FF
ROM:B22A sta $6002
ROM:B22D lda #$7F
ROM:B22F sta $6003
ROM:B232 lda #$FF
ROM:B234 sta $6004
ROM:B237 lda #$64 ; 'd'
ROM:B239 sta $6006
ROM:B23C lda #0
ROM:B23E sta $6007
ROM:B241 lda #0
ROM:B243 tax
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: Matt Ownby]
#382976 - 07/03/19 11:37 PM
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: Matt Ownby]
#382982 - 07/04/19 07:43 AM
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I can't help with your question, but I do want to thank you for your efforts! I'm a big fan of the laser disc era and I'm really glad to hear the discs are being archived!
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: italiandoh]
#382983 - 07/04/19 01:40 PM
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It would be nice to have a solution also for the LD-V4300D, as it's the Domesday86 reference player.
I'll soon set up a Domesday86 with a LD-V4300D for dumping some arcade discs and I'm starting to worry about this issue.
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Re: [LASERDISC] What CPU is this? what machine language instruction set does it use?
[Re: ClawGrip]
#382987 - 07/04/19 10:28 PM
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> It would be nice to have a solution also for the LD-V4300D, as it's the Domesday86
> reference player.
>
> I'll soon set up a Domesday86 with a LD-V4300D for dumping some arcade discs and I'm
> starting to worry about this issue.
considering the investment in the tech so far I don't imagine patching a firmware is going to be the greatest hurdle.
I mean, MAME can emulate actual Laserdisc players, the Laserdisc player in question is a potential candidate for a standalone driver, debugging the firmware is possible.
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