Instruction Register PCB working

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 11/09/2018 at 11:010 Comments

Finally build the IR PCB and it works fine.

One issue: I forgot a pin header and had to make an ugly workaround:

Other (small) problem: the green leds are very weak (look the led bar at top, it is showing the 01010101 pattern). I measured the 74ALS874 output and it reads only 3,5V, and while it is still inside the TTL standard, I am used with 5V on outputs. So I will need to lower the resistors but it is a simple and painless change.

TTL accepted voltage levels:

Image result for ttl voltage levelsThanks for reading.