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Looking to put some TI TMS99xx chips onto GALs/CPLDs


dirty-harry

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Hi.

 

As some TMS99xx chips are getting harder to source, I was thinking of popping some of them (their functionality at least) onto GALs/CPLDs. I was thinking of putting :

 

TIM9904 (aka 74LS362) Clock Generator

74LS612/610 MMU

TMS9901

TMS9902

 

Possibly TMS9901+TMS9902 + MMU all onto one chip ?

 

 

Has anyone done this before or got HDL code / boolean equation for their functionality ??

 

Thanks

 

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Combining them all into one chip might give you some serious available pin issues and force you to one of the larger CPLDs, negating much of the advantage you gain price-wise. The 74LS612 and the TMS9901 are 40 pin packages--and they use them. There are only a few that can be cross-utilized. The same goes for the TMS9902, although that is a much smaller package.

 

Most of the chips show up pretty regularly in any event. When I need larger quantities, there are a lot of wholesale parts vendors with access to some serious quantities out there--though pricing can be a bit bad unless you order a lot of them. . .

 

The idea to make modern equivalents isn't a bad one though--but I haven't seen files for any of the chips you've identified here out in the wild. You'd probably have to start from the beginning and develop your own--though you might be able to use the MAME emulator to validate exactly what each of them is supposed to be doing.

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Combining them all into one chip might give you some serious available pin issues and force you to one of the larger CPLDs, negating much of the advantage you gain price-wise. The 74LS612 and the TMS9901 are 40 pin packages--and they use them. There are only a few that can be cross-utilized. The same goes for the TMS9902, although that is a much smaller package.

 

Most of the chips show up pretty regularly in any event. When I need larger quantities, there are a lot of wholesale parts vendors with access to some serious quantities out there--though pricing can be a bit bad unless you order a lot of them. . .

 

The idea to make modern equivalents isn't a bad one though--but I haven't seen files for any of the chips you've identified here out in the wild. You'd probably have to start from the beginning and develop your own--though you might be able to use the MAME emulator to validate exactly what each of them is supposed to be doing.

There's quite a few low cost CPLDs out-there nowadays so that's no big problems and they are all faster than the old 74 TTL/CMOS chips . The 74LS612 has a 40ns propagation delay.. so a faster version of that (10ns) would be good. though I'm not sure how much I could squeeze into say a EPM7160SLC84 ?? Plus having ALL peripheral ICs on one chip would seriously cut down on board complexity and cost !

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... The 74LS612 has a 40ns propagation delay.. so a faster version of that (10ns) would be good. ...

What does that get you in this case? The system clock on all these classic computers is well below 10MHz in all but a few cases (some 12MHz over-clocked systems pop up every now and then.) Even at 4MHz the clock cycle time is 250ns, which leaves plenty of room for other combinatorial logic in the address decoding path.

 

... though I'm not sure how much I could squeeze into say a EPM7160SLC84 ??

How much you can squeeze depends on how many gates you need to describe the original functionality and how well you utilize the CPLD's or FPGA's logic blocks.

 

Plus having ALL peripheral ICs on one chip would seriously cut down on board complexity and cost !

I don't know about that. It was already pointed out that you are talking about re-implementing a lot of 40-pin DIP packages, so your CPLD/FPGA I/O count is going up really fast. You are going to be into a BGA package for sure, so you are now talking about a 4-layer PCB minimum to support the escape routing necessary.

 

IMO a much simpler approach would be to get an SMD to DIP adapter board and use a programmable logic device to re-implement each original chip individually.

 

Sounds like a GOOD idea...if it can be done ?? You could then possibly make a complete TMS99xx system with 10 Chips (or less) !!

At that point, why not just make the whole system using an FPGA? With all the major components re-implemented in programmable logic, the only thing you would be doing with the PCB is implementing the top-level in a typical FPGA SoC design. To me, this actually makes the project harder.

 

The over-all goal was never stated other than it seems hard to source some of these older ICs. To keep an existing system running, the SMD to DIP adapter with dedicated programmable logic would be the cheapest and easiest, IMO. If the goals are to make a new custom/unique system, then I guess it does not matter. But trying to cram a lot of these pieces into a programmable logic device, but stop short of the top-level routing, does not make sense to me and only makes it harder.

 

Anyone who wants to see what is being done with discrete-logic in the hobby-space these days:

 

http://www.homebrewcpu.com/

 

http://forum.6502.org/viewtopic.php?f=4&t=3329

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