Tuesday, 10 July 2012

About the Project

This entry for the retrocomputing challenge is to recreate the NRI832 computer, first in software, then in hardware.  

The big question - what is an NRI 832 ?

It's pictured on the right.

It's one of the first - possibly the first - home computers you could buy or build, along with things like the Mark-8, Educ-8 and Kenbak-1.

It was sold as a DIY kit, for $503, as a teaching computer. Unlike many of the courses available at the time though, it is actually a computer.

It is entirely built out of standard TTL Logic gates, about 75 of them, so you could actually build the real thing. I won't do it that way, I will reproduce it using more modern hardware - probably an Arduino. The main reason is I do not fancy wiring up the 128 switches - I'll use one of those cheap keypads instead.

It comes in two variations ; one has no RAM and 16 byte of ROM, the other has 16 bytes of RAM added.  You can still 'store' on the original, it just stores to the internal register instead.

The ROM is the array of switches you see on the picture - you 'program' it by setting each switch to the binary pattern.

The CPU (which is a serial processor) has 3 8 bit registers A,B and E, and an instruction set with 16 instructions - 7 of which have a single operand, and 9 of which have no operand.

It operates at 250Hz (fast mode) or 2Hz (slow mode)

Next thing to do is to read the available documentation. There were three manuals, but only two are available - the schematic and the construction manual. There was also an "11k Reference Manual" which I would guess was the training guide, but I've not been able to find it. All contributions accepted :)


The Circuit Diagram
The 10k Reference Manual

Picture (courtesy of OldComputerMuseum.com which also has some historical information)

1 comment:

  1. Wow! Nice job Paul! I appreciate your efforts in putting together all this data on the NRI832. I actually had one of these. I had trouble with the power supply and kept burning out bulbs. It's nice to see the emulator and not have to worry about getting new bulbs for the blasted thing. Most likely I did something wrong in the soldering process and caused the fault myself. I will see if I still have the old manual. It might be buried in my stack of electronics books.
    Peter Conrad