CPLD to replace 74xx chips in an old circuit

[ebastler]

Thanks, but with the answers that I have read I already realize the options that I have from a technical point of view, leave everything as is, CPLD or FPGA.

Other factors of an economic or commercial nature are not matters that I have considered to treat them publicly.

Right now, I just want to leave the circuits as they are or replace the 74xx chips with a CPLD, nothing more. Maybe in the future, and if there is no other option, consider migrating to an FPGA that replaces the processor and 74xx chips.

If you feel comfortable making that judgement call, that's fine of course. Your approach implies a limited design effort and somewhat limited design life due to the already aging components. There certainly is a range of expected product lifetime and quantity where this makes good sense. Best of luck with the project!

[zitt]

If you look at his signature... he lists a facebook page which looks to be a company whom designs boards for pinball machines.
I'm only guessing; but he's probably considering replicating Pinball "boards" which typically has 10s/20s of TTL chips on them... tied to a 6502/6800/68000 cpu and maybe some older PIAs.

Again; I'm guessing he's having trouble sourcing the older TTL and is looking for find another way of getting form/fit/function equivalence without reverse engineering the operation of said boards and ensuring 100% compatibility with the game "software".

Again; this is all a guess based upon what us a-typical Pinball Nerds tend to do for fun. Case in point:
http://pinball-mods.com/blogs/?p=278
I need to get back to this project... can someone teach me how to sleep less with no heath impact?

Not sure if he's trying to be vague to keep people out of his sandbox... or if it's a language issue... or what.

[FrankBuss]

For pinball machines, you could just use any modern ARM microcontroller, no need for high speed logic gates or FPGAs. Of course, you would need to re-implement the code for the 6502 etc., but this might be even a good idea, you could do it in C, it would be easier to maintain than the probably in assembler coded old CPU code.

[zitt]

It's a software porting excersize which many hardware hackers have issue with.
I'm not saying it's not doable... it's just a different methodology that many people don't want to do.

There are plenty of examples of pinball people who start "re-implementation" projects only to end up doing their own thing.

I actually went down a rabbit hole recently of trying to disassemble a modern ARM design from Stern. I think this was the thread which started me down that path: https://www.avrfreaks.net/forum/trying-disassemble-and-am-super-confused
.. but the premise is that I wanted to disassemble the game ROMs so that I could "patch" it to add the ability to turn on a specific transistor during a specific game mode.

I spent several hours... or maybe a day or two trying to find a working, free (opensource) de-compiler for the ARM which ran it windows.  IDA Pro licensing wasn't something I was going to "buy" without a working trial and some confidence would get me to the end goal.

[T3sl4co1l]

Port? Heck, just emulate it.  Some very good 6502 emulators out there after all; just patch on the correct bus devices and write the interfaces for the new devices.

Tim

[FrankBuss]

Right, emulating it would be possible, too. It is possible to emulate a full C64 with a slightly overclocked STM32F4 microcontroller:

https://hackaday.com/2014/10/23/a-complete-c64-system-emulated-on-an-stm32/

The VIC for the graphics output would be really complicated, but if you don't need this, a bunch of old CPUs instead should be no problem to emulate. But not as elegant as re-writing it from scratch in C, which has the additional benefit that it can be used for other pinball machines as well, or for implementing other game modes or easier changing existing game modes.

[james_s]

I'm a fan of using FPGAs for this sort of thing, I've been doing that with early video games, the hardware is similar but pinball hardware is not very interesting without the rest of the machine. I have recreated several sound boards from pinballs though.

[guenthert]

The jump from implementing a bit of logic in a CPLD to building a whole system in a FPGA is not as large as it first seems, because there are already tested working softcore CPUs and complete systems available.
[..]

Keep in mind that this seems to be an embedded system (regardless whether or not it is a pinball machine), there you're likely to encounter bit-nibbling and other time critical tight loops, particularly if among the support chips there is no counter (the original Z80 didn't have counters).  So unless the simulation is cycle-perfect, there is a good chance, it won't work.

How difficult is it actually to source the 74xx chips?  I see them still here and there, e.g. https://www.jameco.com/c/ICs-Semiconductors.html

[luiHS]

How difficult is it actually to source the 74xx chips?  I see them still here and there, e.g. https://www.jameco.com/c/ICs-Semiconductors.html

There is no supply problem, all 74xx are available. The idea is to make a more compact design, in which all 74xx are replaced by a single CPLD.

[james_s]

There are some cycle accurate soft cores out there, I know there's one for the 6502, and the 6809, I'm not sure if there is a cycle accurate Z80 and I have not been able to find a cycle accurate 6809. For most old arcade hardware this doesn't seem to be an issue, some boards have a timer IC, the 6532 RIOT is common on 6502 boards. Some do not though, the sound board that Williams used in a number of pinballs and video games uses a 6800 variant and the cycle inaccuracy causes some of the sounds to play at the wrong pitch. 

[meandeev]

There is no supply problem, all 74xx are available. The idea is to make a more compact design, in which all 74xx are replaced by a single CPLD.

I like this Idea! I like to repair old measurement gear full of logic IC as a hobby. So I have boxes of boxes full with 74xx. But never the one that I need for the recent project  :-)
So for a first test (or a full repair) it would be nice to have such a "universal" IC.

I found https://www.eetimes.com/document.asp?doc_id=1274659#, but the company doesn´t exist anymore.

One could buy it in 2012 https://web.archive.org/web/20120323140407/http://www.retrodevices.com/

but it was really expensive (why?) https://web.archive.org/web/20111104181944/http://www.retrodevices.com/rdttl5515.html

Again, I would be happy to throw away my 74xx boxes that never( or seldom) have the IC´s that I need for the current project - having a few universal chips.

So a XC9536(XL) and a board would do it, isn´t it?

[zitt]

There is no supply problem, all 74xx are available. The idea is to make a more compact design, in which all 74xx are replaced by a single CPLD.

Wonder what world he lives in?!
https://www.digikey.com/products/en/integrated-circuits-ics/logic-gates-and-inverters
is not what I would call readily available.

Just because you can buy 7400 series logic on the secondhand market - does not mean you can get large volumes of these ICs for build a "new design". By all means; If you have a source for NEW 7400 series logic available from a major manufacturer please share. It's my understanding that 7400 series logic has been EOLed by nearly every major manufacturer. I don't think there are any "drop in" replacements.

[SiliconWizard]

Indeed. The more readily available ones are the various later series such as HC, HCT (and still not all), and much more recent such as LVC, AUP and so on... but basic 74xx? Not really!

[mariush]

I wouldn't do it ...
I mean if you buy these parts in volume, they're maybe 10 cents each ... so your parts cost less than 2$ for each circuit...and you're gonna replace them with a 4$+ chip?

Is it a space issue? if so there's versions of these chips in packages like 14-VFQFN (ex 74HC04BQ,115 or 74HC00BQ,115 so you could squeeze a bunch of these ICs in a tiny area, compared to DIP or SOIC versions of these chips.
To reduce space, you could make double sided tiny boards with 4 or more such chips, and have a 0.1" or 0.05" header on one side or both sides (like a dip chip).
You could make these tiny boards in 4 layers if you want to, to reduce trace lengths and so on ... make a big board at a chinese manufacturer and use v-scoring to cut these tiny boards from a big panel, if you need volume.

[digsys]

Contrary to others advice, I've done a lot of this recently - I've got back into repairing old plastics injection machines and various other types industrial machines.
I get at least 1-2 weird PCBs a week, full of "glue" logic and then out to bus-frame connectors / specialized I?F etc
The easiest / best approach I found is to trace out all the "glue logic", rebuild it, either an adapter PCB or CPLD / GAL etc and sometimes by an MCU. It takes a day or 2 to work out the logic, but it's well worth it. The "BIG" one, I've been working on for weeks has dozens and dozens of glue chips / MUXes etc, but it'll be worth it.
I actually like this sort of challenge - horses for courses.
Where are you up to? Decided on a part yet?

[luiHS]

 
Finally I have not complicated my life with the solution of the CPLD, I have designed the new board with the original schemes, but I have reduced the size of all the components, and all that have been possible, which are the majority I have put SMD ( on the original board are all THT).

All the passive components are now 0402, the 74HCxx in TSSOP, PAL in TSSOP, the eprom in PLCC32, the crystal of 3.2x2.5mm and the RAM that is now in SOIC I will replace it for a TSOP.

The processors have not been able to reduce them, the TS68000 stays in PLCC and the other processor in DIP mounted in socket. As I assemble all my boards with my own Pick and Place, a Neoden4, assembly time is not a problem, it is very fast and convenient.

However, I would like, when I have time, to learn how to program CPLD, I'm sure I give it some use with new designs, or to redesign old boards.

[mariush]

Looks nice.

I don't really agree with the use of 0402 resistors and capacitors ... it's pointlessly small, making difficult to rework a board if there's an issue. It's not like a 0603 part would affect the layout, there's plenty of room.
Also not a very big fan of those surface mounted electrolytics - I'd be concerned about vibrations and about someone accidentally hitting those and have them fall off the board.
It wouldn't cost you anything to add through holes in parallel with the surface mount footprint for those two capacitors, so you could install electrolytic capacitors flat, like time crystals if you wanted to (with a drop of selastic/glue material to hold it and reduce strain of leads in case of vibrations.

[luiHS]

Looks nice.

I don't really agree with the use of 0402 resistors and capacitors ... it's pointlessly small, making difficult to rework a board if there's an issue. It's not like a 0603 part would affect the layout, there's plenty of room.

Thanks.

I cannot have in my Pick and Place machine, the same component value in several sizes, the space for reels is limited and I am already running out of space. 0402 because I have designs in which that size is necessary, and that it can be used perfectly on any other board.

Also in tubes and reels, they occupy much less TSSOP chips than SOIC, in the Pick and Place. I reduce everything in size, and for now they are all advantages.

The Neoden4 is working very well for me to put 0402, I could even put 0201, but with 0402 I have enough for everything I design, for now. For me, definitely, 0402 is the best. I have no problem checking my boards, even to repair any, I always use the microscope, optical for repairs, and the electronic to check welds.

Also not a very big fan of those surface mounted electrolytics - I'd be concerned about vibrations and about someone accidentally hitting those and have them fall off the board.
It wouldn't cost you anything to add through holes in parallel with the surface mount footprint for those two capacitors, so you could install electrolytic capacitors flat, like time crystals if you wanted to (with a drop of selastic/glue material to hold it and reduce strain of leads in case of vibrations.

I manufacture many boards and I need to optimize time and comfort to the fullest. Everything that is SMD is welded in the oven and does not require any special manual treatment, which always means a waste of time.

I have stopped using THT components for quite some time, except for some power connectors, and the time and comfort savings are maximum. I would not go back in any way to the times of doing it all with THT, even using solder pot, just for convenience it is infinitely better to use SMD.

[legacy]

I would not go back in any way to the times of doing it all with THT, even using solder pot, just for convenience it is infinitely better to use SMD.

Except, when some chip is damaged or has some quirks (1) and you have to desolder it. SMD is bad in this case.

(1) quirks
Example1: someone at Palm decided to program the flash of their PDA with write protection set only for the second block, which makes no sense since it contains the graphical Logo and the Copyright. I mean, a malicious program running in the PDA can erase the whole operating system, but even if it issues the command "flash_erase_all()", the block2 isn't touched.

Does it meant that the graphical Logo and the Copyright are probably more important than the OS? Who knows, anyway, if you want to hack an old PDA, no way, you have to desolder the flash because it's not possible to unlock the block2 of the flash without applying high voltage to a specific pin, which would destroy the around circuits; and just to make you crazy on something, the SMD-flash-chip has a glue/resin on its back, and it's located too near SMD-resistances and capacitors, which makes the desolder procedure a nightmare   

Example2: the terrible "supervisor chip" that you usually find in a UNIX workstation is also usually SMD and usually prone to die after you have already paid for the good and left the positive feedback to someone on eBay. What does happen when this chip die? The system simply will no more start. And to solve the problem you have to replace the chip.

Now, the problem here is that the chip is usually between two PCI slots, under something, and too near to something that can bend when you apply hot air simply because it's too hard to be protected with tape. Moral of the story ... it usually ends with a cry.

----

How would this end with a DIP-chip installed in a DIP socket?
With you removing the chip in a click. A piece of cake 

[Kjelt]

Except, when some chip is damaged or has some quirks (1) and you have to desolder it. SMD is bad in this case.

I don't know. I also had my share of disaster with TH chips where there were large ground planes attached so you just could not heat the pin enough to desolder it.
We all had the experience that the via's stuck on the pins after extracting the chip etc. etc.

With SMD the cleanest way is to cut the legs with a very small exact cutter.
If the legs are under the chip or BGA you need a hot air gun with specialized nozzle with vacuum cup.
So you need different tools and techniques.

[SiliconWizard]

Yeah. Desoldering TH chips through 8 layers or more (like on motherboards) was often a nightmare, so...

[legacy]

Yeah. Desoldering TH chips through 8 layers or more (like on motherboards) was often a nightmare, so...

DIP chips on DIP sockets, you do not have do desolder them.
You cannot have (cheap) SMD sockets for SMD chips, you have to desolder them.

[wraper]

How would this end with a DIP-chip installed in a DIP socket?
With you removing the chip in a click. A piece of cake 

It will probably end up DOA even before put in operation if sits on the shelf long enough. Using sockets ensures poor reliability. Especially when socket doesn't cost more than IC itself (unless IC is very expensive). And in harsh environments all sockets will suck anyway, just to different extent. When soldered, SMT is way easier to replace compared with DIP.
Using sockets for everything is counterproductive. Only using for some programmable/upgradable chips makes some sense. And even that basically lost justification nowadays, since you usually have some serial interface for in circuit programming anyway.

[legacy]

SMT is way easier to replace compared with DIP.

Neither replacing the SMD-flash on my Palm-PDA nor replacing the Supervisor chip in my UNIX workstation were an easy task, but rather a mess! In fact, this cost me 250 euro (including shipping to them/and back to me, UPS was something like 20+20 Euro) because I was not able to do it by myself, even if I own a semi-professional Aoye Int2703A soldering station with which I have soldered a lot of SMD boards (e.g. the last one Amiga1200 clone), and I, of course, tried to do by myself with those chips to replaced, but then realized that I had better ask someone with better skills and tools, and even the company I paid for the job, said it was a very hard task, especially replacing the Supervisor chip!

I paid something like 210 Euro for replacing two chips, I wouldn't say that it was easier and cheaper than replacing a chip on a DIP socket 

[wraper]

I wouldn't say that it was easier and cheaper than replacing a chip on a DIP socket 

You just would pay upfront 3x the price for boat anchor which probably would fall apart even before delivered.