Close

Weekend update

A project log for JACA 1 & 2 Homebrew Computer

JACA - Just Another CPU Again Homebrew CPU, starting by a simple POC 4-bit CPU on circuit simulator soft. (done), then 8-bit (in progress)

andre-baptistaAndre Baptista 09/05/2017 at 02:420 Comments

v.0.14.0 Big changes.

- Reorganized instructions. As Opcodes changed, all test programs must be reassembled (not finished yet).

- Implemented some new ALU instructions such as XNOR, INC and DEC. Add new ALU instructions is pretty simple, just add new lines to Microcode ROM.

-The main change: now there are two registers called H and  L, which will be used to addressing in Direct By Register instructions, containing the High and Low parts of address. These two fix registers replace the previous idea of use any pair of registers [RR3]. Also added one controlled buffer (called Regs Bridge) to separate the outputs of the registers into R1 (A, B, H and L) and R2 (C, D, E and F). This overcome the old limitation that the ALU operations had to use always A register as first input. Now it's much more flexible, R1 for first input (and output also) and R2 for second input.

New control lines were added to the circuit, and Microcode had to be rewritten.

Maybe I've forgotten something. Hope I didn't...

Very busy (and fun) weekend.

Edit: forgot to mention: all this work only in virtual world (Logisim). Real hardware is stuck as the extras 12 breadboards I've bought still didn't arrive...

Discussions