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An unusual 7400-series chip implemented with a gate array

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Re: An unusual 7400-series chip implemented with a gate array

#21

Post by kens »

pclmulqdq wrote: post #20
francescovv wrote: post #4

> transistors in an orderly matrix (...) forming scattered circuits connected by thin metal wires. That's [ULA], isn't it? This tech was also known as "Gate Array", before FPGA came along. [ULA] https://en.wikipedia.org/wiki/Uncommitted_logic_array

I have heard of this structure also referred to as a PLA - programmable logic array, and I think a ULA is specifically for a PLA that is embedded in the empty space of a bigger design (so that in case something is broken, a debug is one mask, not a full respin). I am not sure that Wikipedia is out-of-date enough to have the precise terminology, but I also may be wrong.

The terminology is a bit of a mess, but usually a PLA is highly structured with an AND plane and an OR plane, so it implements sum-of-products logic. A gate array is more general, with arbitrary connections.

Re: An unusual 7400-series chip implemented with a gate array

#24

Post by WalterBright »

kens wrote: post #7
francescovv wrote: post #4

> transistors in an orderly matrix (...) forming scattered circuits connected by thin metal wires. That's [ULA], isn't it? This tech was also known as "Gate Array", before FPGA came along. [ULA] https://en.wikipedia.org/wiki/Uncommitted_logic_array

Yes, a ULA is another name for a gate array. A while ago I bought an 8086 chip on eBay that turned out to be a random ULA chip that was re-labeled: https://www.righto.com/2020/08/inside-counterfeit-8086-proce...

I was intrigued, thinking that someone had managed to clone an 8086 with a gate array. What a disappointment.

Re: An unusual 7400-series chip implemented with a gate array

#25

Post by WalterBright »

hyperman1 wrote: post #9

Funny to see this appear online today. I was discussing the real nand2tetris computer built from 74 ICs yesterday with my 8 year old son yesterday: https://hackaday.io/project/185131-the-hack-computer-from-na... and now this pops up. I'm thinking of buying a bunch of 74xx ICs and buttons and led+resistors somewhere and let him mess with them. It's stone age digital tech according to current norms, but I'd rather see…

A EE in my dorm in the 70's designed and built his own CPU out of 74xx chips when he was in high school. Even the other students were in awe of that.

Re: An unusual 7400-series chip implemented with a gate array

#26

Post by userbinator »

I couldn't find pictures of a '139 implemented the "normal" way, but here's a 1-of-8 decoder that is: https://www.richis-lab.de/logic20.htm

The dual-die+decoder EEPROMs reminds me of these quad-die EPROMs: https://www.eevblog.com/forum/chat/identify-these-weird-epro...

Are you sure there's not another two 28HC64s on the other side too?

Re: An unusual 7400-series chip implemented with a gate array

#27

Post by kens »

userbinator wrote: post #26

I couldn't find pictures of a '139 implemented the "normal" way, but here's a 1-of-8 decoder that is: https://www.richis-lab.de/logic20.htm The dual-die+decoder EEPROMs reminds me of these quad-die EPROMs: https://www.eevblog.com/forum/chat/identify-these-weird-epro... Are you sure there's not another two 28HC64s on the other side too?

Yes, I'm sure there are just two EEPROMs. Someone on Twitter found the datasheet for the module (DPE8M628), which has details: https://www.datasheetarchive.com/datasheet?id=a3c8d65ff60242...

Re: An unusual 7400-series chip implemented with a gate array

#28

Post by ekimehtor »

kens wrote: post #12
cosmolev wrote: post #11

Earlier quoted context omitted.

Why have you wasted 80% of the die?

I'm not sure what you're asking. IDT used the same gate array for numerous 7400-series products. As a result, simple chips would waste most of the die, while complex chips would use most of it. The tradeoff is that using a gate array saves design costs, although each chip is more expensive to manufacture due to the wasted silicon. Since IDT was selling into low volume, price-insensitive markets (military), the tradeo…

I may be dating myself here but I seem to recall Intel offering a hobbled 486 processor in which the math processor was disconnected for no other reason than marketing. Regarding the Gate array Technology it seems we've come full circle with the new risk V processors being offered up at incredibly cheap prices.

Re: An unusual 7400-series chip implemented with a gate array

#29

Post by ekimehtor »

I know it's not adding very much to the conversation but I just have to give kudos to the author of this article. It's always nice to see what the magic smoke inside those chips look like before I let it out! So great job I look forward to reading more of your articles!

Re: An unusual 7400-series chip implemented with a gate array

#30

Post by cjk2 »

WalterBright wrote: post #25
hyperman1 wrote: post #9

Funny to see this appear online today. I was discussing the real nand2tetris computer built from 74 ICs yesterday with my 8 year old son yesterday: https://hackaday.io/project/185131-the-hack-computer-from-na... and now this pops up. I'm thinking of buying a bunch of 74xx ICs and buttons and led+resistors somewhere and let him mess with them. It's stone age digital tech according to current norms, but I'd rather see…

A EE in my dorm in the 70's designed and built his own CPU out of 74xx chips when he was in high school. Even the other students were in awe of that.

I did that in the early 90s. Was only a 4-bit job but it mostly worked! Edit: it only ever ran one program which was to count to 99.

There is a whole community of these machines: https://www.homebrewcpuring.org

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