Close

Debug Time...

A project log for DDL4-CPU

A Modular 4-Bit CPU Design

daves-dev-labDave's Dev Lab 05/25/2018 at 23:210 Comments

With the Clock Generator Module completed, I was able to begin debugging some of the modules. The PC-IR Module and the Decode Module are the only two modules in the design that were not previously tested as part of another project, so they were my first concern. Both the PC-IR and Decode Modules use a 74LVC193D, which I had not previously used in a project. Unfortunately, I didn't read the datasheet closely enough. I am not using the "down" could features of the 74LVC193D, so I tied it to ground. WRONG! Apparently when the down count is not used it needs to be pulled to VCC. I added wire fixes to both the PC-IR and Decode Modules. After adding some jumper wires to the EEPROM sockets on the Decode Modules to allow for testing, I powered up the boards.... and nothing. The Clock Generator wasn't running. I had already tested the Clock Generator, and knew it was working, but what could be the problem? Turns out the RESET and HALTn signals had gotten swapped on the PC-IR modules, so a second set of wire fixes were needed. After doing a bit of soldering, I was ready to re-test. BINGO! I have the phase counter working, as well as the program counter! Time to move on to assembling the remaining modules!

Discussions