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  • Joined: 08 Nov 2014
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Who made the VDPs
Post Posted: Sat Nov 08, 2014 1:45 pm
First of all, Hi all! I'm a newbie here! I've been interested in SMS for far too long to not be on this forum so decided to join. Hope you don't mind me jumping in...

My first question if anyone is interested in helping is to ask about the VDP. Through leaked service manuals we now know comprehensively that Yamaha manufactured the Master system and Genesis VDPs. But does that mean Yamaha designed them and Sega bought them under some exclusive contract, or does it mean Yamaha simply fabbed them for Sega? I would have said the first scenario until I noticed that NEC manufactured the VDP for the Game Gear (see the service manual, it lists an NEC part).

OK, so we know also that Yamaha cloned the TMS9918 and the nascent TMS9228 and evolved it into the V9938, so it does seem like Yamaha is still the best candidate for designer of the VDP but I'm still left wondering... did SEGA have the in house resources to design their own stuff, or did they just farm it out to Yamaha?
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Post Posted: Sat Nov 08, 2014 1:48 pm
answering my own question somewhat (how crude of me), I just wanted to add that the thing that tips it in the favour of being also Yamaha designed is that the 9228 had it made production was advertised as having an on die PSG, which indeed the Sega VDP has.
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Post Posted: Sun Nov 09, 2014 2:37 am
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I would have said the first scenario until I noticed that NEC manufactured the VDP for the Game Gear (see the service manual, it lists an NEC part).


Speculating a bit here:

Previously the most economical way to make a custom part was to design logic that went into a gate array, which companies like Hitachi and NEC fabricated. The logic was developed exclusively by the customer (Sega) and the gate array manufacturers didn't play a role in design. This was the basis for most custom chips found in arcade games because it was comparatively cheap and fast to develop. The downside is that you were limited to whatever functionality the gate array had - regular logic, small ROMs and RAMs, etc.

For more complicated chips like the SMS and Genesis VDP you pretty much had to have another company do all the design work. I assume Sega had some high level specifications for Yamaha, who then were free to implement the low-level parts in whatever way met those specs, and then fabricate the chips for Sega's consoles to use. As trivia the SMS I/O chip which is considerably less complex is a NEC gate array, whereas the VDP isn't.

For the Game Gear, if you look at the VA1 schematics they refer to the chip NEC made as a "custom chip". Inside it has an entire Z80 and VDP block (from Zilog and Yamaha), and then a standard cell array, which is the part that is analogous to gate array design in terms of having predefined parts to put together as you see fit. So Sega's engineers could develop the logic that ended up in the standard cell array, which in turn interfaced with the Z80 and VDP blocks that they didn't directly design. Then NEC fabricated the resulting chip, again without playing a role in terms of design.

You see this a lot in the later Genesis 2 and 3 system which had a huge amount of integration towards the end. Sega could include these fixed-function blocks (68000, Z80, YM2612, VDP), add their own glue logic, and have a company like Hitachi or whomever make the chips. It's safe for Motorola and Zilog as they are providing these blocks as completed units rather than giving Sega low-level details about the inner workings.

For example you can still get a 65C02 component from Western Design for inclusion in an ASIC. To you (the designer) it's a black box with some inputs and outputs, and when you get your chip made it will have this fully functional 65C02 CPU in it connected to the other logic you designed.

So the short answer is that Sega probably did the design work for their gate array and standard cell-based products themselves, and relied on companies like Yamaha to make complex parts like the VDP on their own within the parameters Sega defined. The GG ASIC ends up being a Sega design (VDP specification and standard cell array), implemented by Yamaha (VDP) with components from Zilog (Z80), and manufactured by NEC.

I guess we could get more conclusive answers if the chips got decapped and we could look for identifying names and part numbers on the die.
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Post Posted: Sun Nov 09, 2014 2:02 pm
I don't want to derail the topic but... I am wondering what's inside an SMS VDP. I mean, is there a sort of 'small' specialized microprocessor executing a 'simple' program written somewhere in a small ROM inside the same chip or is it just gate logic?

edit:and, in topic, there are no chances to ask such questions to someone who worked for SEGA at the time? I mean, maybe someone can be reached thru e-mail or thru some social network probably...
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Post Posted: Sun Nov 09, 2014 5:28 pm
Excellent and comprehensive answer, I think you likely nailed it there Charles. You're kind of a personal hero of mine for your excellent docs on the VDP already :)

I've been putting together a formatted version of your VDP ASCII documentation and would love permission from you to publish this, of course I would let you see it all beforehand so that you were happy with it. PM me if you like.

Quote

I guess we could get more conclusive answers if the chips got decapped and we could look for identifying names and part numbers on the die.


Yep, I think it would be great to send a VDP to the visual 6502 guys and a bit of cash to get them going, they've done amazing work so far. When I'm back on my feet financially I'd be happy to contribute, looking for work at the moment.
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Post Posted: Sun Nov 09, 2014 5:39 pm
sverx wrote
I don't want to derail the topic but... I am wondering what's inside an SMS VDP. I mean, is there a sort of 'small' specialized microprocessor executing a 'simple' program written somewhere in a small ROM inside the same chip or is it just gate logic?


Just gate logic as I understand, it is derived from the TMS9918 but extends it in important ways.
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Post Posted: Fri Aug 30, 2019 4:41 am
Hey, I'm unsure if there's rules against bumping or not. But I didn't want to duplicate a thread needlessly.

Is it known if it was just Yamaha that manufactured the Master System VDPs? Or did multiple companies manufacture it?

This question comes about due to some discussions in a Mega Drive channel finding that both Yamaha and Toshiba have manufactured VDP/ASICs for SEGA.
So, I - and some other people - are curious if such an arrangement had ever occurred with the Master System too.

EDIT: Disregard this post - I assumed Yamaha literally fabbed the VDPs, rather than just designed them.
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Post Posted: Fri Aug 30, 2019 5:23 pm
SMS1 VDP is Hitachi made Yamaha part YM2602, SMS2 VDP is NEC manufactured part µPD9004. MD VDP Yamaha part YM7101, made by various Japanese manufacturers (i.e Sharp, Hitachi...)
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