semi-homemade micro

[gordonjcp at gjcp.net]

> On 11/14/2005 at 5:57 PM Jim Battle wrote:
>
>>>"The PDP-8 was a 12-bit computer with 4096 words of memory. It had only
>>eight
>>instructions, one full register, the accumulator (AC), and a single-bit
>>register, the link (L) bit. The machine operated at a clock rate of 1
>> MHz,
>>and
>>took  10 clocks for each instruction, so that it ran at 0.1MIPS."
>
> Time to add some commentary to the wiki, methinks.
>
> IIRC, the cycle time of the original straight 8 was 1.5 usec.  Instruction
> times in cycles is given here:
>
> http://www.cs.uiowa.edu/~jones/pdp8/refcard/65.html

I dug out the code for my original PDP8 emulator, which was written in
assembler on an 8MHz 8086 PC.  In order to give the CPU a chance to
actually execute some instructions between interrupts from the emulated
teletype, I bumped a counter every time I went round the main loop.  I
found that about 100 instructions gave a suitable (maybe a bit slow) 10cps
terminal speed.

That suggests to me that about 1000 instructions per second is possible on
a slowish machine.

Gordon.