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Is there such a thing as a low pin-count eeprom IC that can be used to replace logic circuits with just a couple of inputs and outputs? I'm thinking of DIP-16 or smaller, but it needs to be parallel.

I'm aware of DIP-8 serial eeproms but unless I'm missing something, this would make things more complicated than using dedicated logic ICs.

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    \$\begingroup\$ Do you mean you want to implement a LUT with EEPROM? It's pretty much a PLA. \$\endgroup\$ – Eugene Sh. Feb 1 '18 at 19:19
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    \$\begingroup\$ I would go with some small CPLD. \$\endgroup\$ – Eugene Sh. Feb 1 '18 at 19:22
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    \$\begingroup\$ "DIP" and "tiny" not really synonyms these days. When you say "tiny" I think of 5 x 5 mm and smaller, chip-scale packages, and 0201 passives or smaller. \$\endgroup\$ – The Photon Feb 1 '18 at 19:23
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    \$\begingroup\$ I was referring to the pin count, not the package size. I can see how this is confusing, I'm not shure how else to describe it, though. \$\endgroup\$ – Joel Hamme Feb 1 '18 at 19:27
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    \$\begingroup\$ Take a look at PALs as well, as CPLD might be an overkill. \$\endgroup\$ – Eugene Sh. Feb 1 '18 at 19:30
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Yes.

For simple tasks, there's PALs and GALs like the 16V8. These parts have fallen out of fashion, but they're still quite functional for hobbyists.

For more complex tasks, consider a CPLD, like the Xilinx Coolrunner-II series or the Altera MAX series. These parts are more complex, but can be used to build much more complex logic than is possible in a PAL.

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  • \$\begingroup\$ The downside of CPLDs is they tend to come in unfriendly packages. \$\endgroup\$ – Peter Green Feb 2 '18 at 3:54
  • \$\begingroup\$ @PeterGreen Depends on what your idea of "unfriendly" is. VQG44 isn't all that bad, for instance. And you can get them on DIP-compatible adapters if you really want something you can stick into a breadboard. \$\endgroup\$ – duskwuff Feb 2 '18 at 4:01
  • \$\begingroup\$ I don't find SMD to be particularly unfriendly, except for breadboard prototyping, of course, and soldering them onto adapters should be easy enough even for beginners. \$\endgroup\$ – Joel Hamme Feb 7 '18 at 15:38
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There was a company called Silego that made very unusual mixed-signal programmable ICs that were tiny and cheap. Besides several small look-up tables, it has comparators, voltage references, counters, an RC oscillator, flip-flops, and you could program how all these blocks were wired together internally. And prices were quite good, in the tens of cents or less for large volume.

Last year they became part of Dialog Semi. Here's one of several parts: https://www.dialog-semiconductor.com/products/slg46120

Perhaps you will find this type of unusual solution useful.

Otherwise, you might consider an 8-pin MCU from Atmel, Microchip, etc. Those are inexpensive and widely used.

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  • \$\begingroup\$ +1 Good find. And at least with some reasonable open documentation, unlike the secretive Lattice stuff. Thanks for sharing. A little problem with availability/pricing though. \$\endgroup\$ – Ale..chenski Feb 1 '18 at 23:35
  • \$\begingroup\$ Glad it's useful. I met these guys and thought they had a really nifty product. Thought they would go public and I would buy up a bunch of shares cheap and make a fortune. Dialog bought them so I'm still an engineer by day. \$\endgroup\$ – Vince Patron Feb 2 '18 at 17:42
  • \$\begingroup\$ I find MCU a bit ambiguous in this context, are you referring to full-on microcontrollers? That is definitely overkill for my application but generally a good idea for low pin-count (thanks!) complex logic. \$\endgroup\$ – Joel Hamme Feb 7 '18 at 15:13
  • \$\begingroup\$ The Silego stuff is not an MCU. It's LUTs, flip-flops, counters/delay, oscillator, reference voltage, comparators that you wire together (via programming). You only asked about the combinational logic of your design, but I thought this might be useful. Besides implementing your combinational logic, it can do some of the analogy, simple state machine, PWM type stuff, all in one cheap IC and might be a more complete solution for you and you haven't looked at before. This is kind of an oddball IC but useful and most engineers don't know it exists. \$\endgroup\$ – Vince Patron Feb 7 '18 at 19:23
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I have exactly the same problem, a simple few inputs into some few outputs. I ended up with chips from configurable multi-function tiny logic, SN74LVC1G57/58/99. For more complex logic the 16V8 is ok, but it is an old-fashion 5V design, no LVCMOS compatibility, no hysteresis on inputs.

The smallest CPLD I found is the Lattice iCE40 family, down to as small as 1.4 mm x 1.5 mm with 16 pins (but really pitchy, 0.35 mm BGA), to a more normal QFN32 (0.5mm pitch, 5 x 5 mm). Nice thing is that the chip has several (3 at least) pins that can drive 24 mA, which makes it a good RGB LED driver with a lot of functionality.

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    \$\begingroup\$ +1. "0.35 mm BGA" sounds like a production nightmare. I have enough trouble with 0.5mm QFN with a thermal pad. \$\endgroup\$ – Wossname Feb 1 '18 at 21:53
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If you have 5x5mm and $5 to spare you can get a small FPGA in that form factor 32-UFQFN eg. Lattice Mach02 series.

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A long time ago, when designing bespoke DSP hardware based around multiplier-accumulator chips (before the days of integrated DSP processors) I used small 8 bit PROM devices to provide microcode sequencing signals. These were driven by a simple counter that drove the address lines to output the timing signals on the data lines. The devices were 16 or 32 by 8 bit capacity IIRC from Signetics. Not sure if devices this small are available but I have seen 8K by 8 devices with parallel data output that could be used to generate 8 arbitrary outputs from up to 13 input lines.

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