Instruction set

A project log for Kobold K2 - RISC TTL Computer

A 16 bit RISC computer with video display, from just a few TTL and memory chips.

roelhroelh 09/13/2019 at 13:460 Comments

This is the envisioned instruction set. It is not complete, several instructions have to be added.

Several things that are possible, are not in the overview. For instance, there is no INC for a data register but it can be incremented by adding #1 to it. Logical OR and AND are possible by combination of CPL and NOR instructions. 

For subtracting, one of the operands must be complemented (CPL) and then incremented (INC) to obtain the 2-complement, and then both operands must be added (ADD). There is a ADDI (add and increment) available, so the INC and ADD can be a single instruction.

A jump is a MOV to the program counter (A0). To do a call, you must store the programcounter (in a data register) and then do a jump (exact call system to be discussed later).

[ edit: the instruction set has changed, see New Instruction Set ]