One-bit Computing at 60 Hertz

More on that one with a VHDL description too:

http://www.brouhaha.com/~eric/retrocomputing/motorola/mc1450...

Handbook has this interesting statement: "When a job is dominated by calculations or data logging, a multi-bit processor is more appropriate. When the task is decision and command oriented, a one-bit machine is an excellent choice."

I'd like to see that put to the test with a number of simple, control systems to see how it measures up. Plus, I'd love to see the demoscene have a go at 4- and 1-bitters to see what they're really capable of.

Thanks for your interest in my projects, 6502nerdface. You've linked to the "chatty" KK article but there's kinduva TLDR version, which folks may prefer, here [1]. In particular the block diagram covers a lot of ground.

Regarding the One-bit computer: although that writeup is a few years old, it so happens that I tweaked a rewrote a few bits just few days ago! I'm pleased by how much attention it has attracted since it was first published. (At the same time it's startling that the mere mention of MC14500 left some apparently inattentive readers with a false impression. What I built is NOT a '4500 machine!)

[1] http://laughtonelectronics.com/Arcana/KimKlone/Kimklone_shor...

not to in any way denigrate the design. its very cute an clever for simple controller applications. but it really kind of folds a few functions in the ur-instruction with reasonable interpretations that turn part of the machine into a nop.

the only part of the design that bothers me is the 2716. i think i've been spoiled by lots of years of having micro controllers one could program with a general purpose communications channel (hc11 shoutout)

i have to imagine this would be a great introduction to processors for non-specialists. a 20 chip ttl design with instruction decode and a register file and address multiplexing is beyond a lot of people's interest.

all those things are really here in concept though, just small enough that you can fit all of them in 8 bits.

thanks for posting that

This seems to be essentially a programmable state machine. You have a series of inputs, states encoded in program memory and a series of outputs. In a real computer, the whole state machine is usually constructed of gates and flip flops and tightly optimized. If fact a typical processor would contain hundreds of thousands of little state machines doing things like sequencing or flow control between different modules.

I don't think such a design would scale up. You cannot put 32 of these together and make a powerful 32-bit computer. There are lots of operations where the bit positions would need to interact. For example an adder where the carry bit must ripple between the bit positions.

Now which is better, this 1-bit computer of a 32-bit computer? It depends on what you want it to do. If all you want to do is take some switch inputs and turn on control some lights, maybe the 1-bit computer is simple, reliable and low latency. But what if you wanted to blink the lights or add some timer delays and suddenly that 1-bit computer doesn't meet your needs without adding a timer source.

First of all the machine should have enough RAM to hold the numbers you want to add. Say two 3-bit numbers a and b:

    a2 a1 a0
  + b2 b1 b0
  ----------
  = c2 c1 c0

Then to do the addition by testing one bit at a time think like

  if (a0==0)
    if (b0==0)
      c0 = 0;
    else 
      c0 = 1;
  else
    if (b0==0)
      c0 = 1;
    else 
      c0 = 0;
  ...