Author here if there are any questions...
Why have you wasted 80% of the die?
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
#12Author here if there are any questions...
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 tradeoff was worthwhile.
Re: An unusual 7400-series chip implemented with a gate array
#13Re: An unusual 7400-series chip implemented with a gate array
#14Re: An unusual 7400-series chip implemented with a gate array
#15Funny 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…
do it. you can use them all for basic synth building too. sequencers and square waves are stupidly easy to build
Re: An unusual 7400-series chip implemented with a gate array
#16Author here if there are any questions...
Why have you wasted 80% of the die?
Why use a $20 Arduino when you could have just gotten a $1 custom PCB, $0.50 microcontroller, and a handful of jellybean parts to do the same job? Because one costs less in Non-Recurring Engineering (NRE) than the other, you'd have to design the schematic and layout and then select parts that are affordable and available. Sometimes its just makes more sense to use a reusable component than doing something custom, especially when you don't plan to sell a lot of them. Someone needed a 1-to-4 decoder and for some reason, couldn't find one on the market that fit the application. The Gate Array already existed and was cheap to configure so that's what they went with. It's overkill but so is getting a brand new die made for such a throwaway part of the design.
Re: An unusual 7400-series chip implemented with a gate array
#17Funny 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…
That’s how I got started — 7400 TTL chips are very forgiving to a young person’s hand.
I was amazed you could just write away to National and the day’s send back a databook! I would pour over them and think of ways to use various chips.
Re: An unusual 7400-series chip implemented with a gate array
#18Funny 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…
Vintage X-in-1 kits. Particularly the 300-in-1 kit had a breadboard and a bunch of logic chips. 500-in-1 similar but even has a microprocessor.
Re: An unusual 7400-series chip implemented with a gate array
#19> 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 it's a primitive form of gate array.
The thing is gate arrays are sort of something between a full custom part and an FPGA, they cost less per chip than a gate array, but more per chip than full custom. On the other hand NRE (up front 1 time cost)) is a lot lower than for full custom (I've built both).
These parts are mil-spec which means that their volumes will be lower, it may have made sense to build a mil-spec pad ring then spin out a range of low volume mil-spec 7400 parts from it
Re: An unusual 7400-series chip implemented with a gate array
#20> 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.