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Revisiting the NS32016

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In 86 or 87 I built a board around the NS32016 CPU, NS32201 TCU, NS32082 MMU, and NS32202 ICU.  (I didn't have an assembler so also wrote a very simple one for it to generate a bit of test code.  Hosted on a VAX and written in DEC macro assembler, which I was very familiar with.)  It also had two MC6850L UARTs.  I never wired up the SRAM, but it worked fine.  It had a socket for the NS32081 FPU, but I don't recall if I had that or not.  I got the chips from a friend at NS handing out samples.  The other day I found the board in the basement!!!  It was broken (veroboard is pretty fragile) but all the ICs seem fine...  It's mostly just 6MHz parts, so nothing fancy super fast.

So... I'm thinking just for the heck of it I'll reuse the chipset and whip up a simple board in KiCad.  I'll give one of the UARTs a VPC USB chip.  A simple interface to do 4-bit SDIO for storage.  4Mx16 3.3V PSRAM with level conversion buffers.  All the random stuff on the board will be SMT to save space, but I'll have two 32-pin EPROM sockets for a simple monitor and boot loader.

I do recall the MMU never worked right, and in hindsight it's probably just awfully buggy.  So I might just leave that out.  I'd only need that if I wanted to get some old version of NetBSD up and running on it... which frankly probably isn't worth the effort.

I used to drool over this processor when it was first announced and waited eagerly for samples. It had a wonderfully consistent architecture for the time.
Trouble was, NS could never make it work. By the time it was available it was too late, Sophie had designed the first ARM processor.

Nice. I barely have any memory of even hearing about them. Did a little bit of looking around and found:

and, especially, , appropriately titled, "The Web Site to Remember National Semiconductor's Series 32000 Family" You might want to check them out if you have not already.

The MMU's datasheet says it provides two hardware breakpoints, so I'd include it even if you don't need its MMU functionality.  If it proves to be excessively problematic you can always disable it by replacing it with a header in its socket, wired to jumper it out.

It took a bit of searching, but all the datasheets could still be found.  I suspect the lack of decoupling might have been responsible for why it was flakey with the MMU enabled... The MMU datasheet specs a power dissipation of 1.5W max and an active supply current of 200-300mA!!! :o  I guess it's really 300mA*5V. No spec for the input capacitance so lord knows, but given the NMOS gate dimensions of this node I'm sure it's pretty major.  This is going to need resistors to keep signals from bouncing all over.

I think I saw on (or maybe somewhere else) that the minimum speed actually is 4MHz despite the datasheet saying 200kHz.  I only had a 2MHz scope at the time and ran it at very low speeds, so that may have had something to do with it as well.  Needless to say in the modern era that's not much of a problem!  :-DD  In hindsight, looking at the datasheets and the very naive design I'm actually surprised it worked as far as executing code out of EPROM without the MMU enabled...

edit: the 4MHz speed is in the errata for the 32016.  The very, very long errata...


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