Intel 4004 was: New To List and PDP8 Question

From: Bill Kotaska <bkotaska_at_earthlink.net>
Date: Thu Mar 13 19:01:01 2003

> You didn't put the programs in RAM, it still require one
> to blow 1702's that you'd replace those on the SIM4 board
> to test out your programs. You need to remember this
> is a Harvard architecture type processor. The motherboard/box. . .
>
Harvard architecture, yes. But the 4004 had a nifty instruction called WPM
(Write Program Memory.) With this instruction - and the appropriate logic -
you can write into RAM and then use bank switching techniques to execute
from it. I use this method along with the 4289 in my 4004 computer to let me
interactively read, write, and execute from any portion of the 16K (bytes)
of RAM. The 4040 expanded on this idea and added a RPM (Read Program Memory)
instruction.

Bill Kotaska
Received on Thu Mar 13 2003 - 19:01:01 GMT