An 8-bit Manchester SSEM Simulator

I sometimes give seminars on the history of computing machines and like to use an Elm simulation of an 8-bit version of the Manchester Small-Scale Experimental Machine (SSEM). The one below is useable and there is a full page version here.

It has a memory of 32 8-bit words, an 8-bit accumulator and a 5-bit program counter. Unlike the original it doesn’t increment the program counter before executing the instruction so is a bit easier to describe and program.

The instruction set and encoding is the same as the original machine.

Inst. Description Encoding
JMP S Jump to address at S 000*****
JRP S Jump to program counter + value at S 100*****
LDN S Load and negate value at S into accumulator 010*****
STO S Store contents of accumulator at S 110*****
SUB S Subtract number at S from accumulator 101*****
CMP S Skip next instruction if accumulator is negative 011*****
STP Stop 111*****