Build 5

The fifth batch of boards contained the first boards for the Index Adder and the XY registers. Updated versions of the PC/SP board and the Output register were also included to address minor errors. A new ALU board was also done to add more status LEDs.

The eleven boards from the five builds can be assembled to form a Turing-complete 8-bit CPU with many of the instructions and addressing modes of a 6502 processor.

X and Y Register and Index Adder

The XY Registers and Index Adder boards passed all self tests and ran test programs with no issues. The design of these was similar to the original NQSAP breadboard build, but the functionality was split between two modules to accomodate the LEDs needed to display three registers and the adder output.

Program Counter and Stack Pointer

The swapped count enable pins were fixed on the Program Counter and the module now works without the need for repair wires.

Output Register

The missing enable pins on the Output Register boards were fixed and the new boards worked as expected.

Results

This shows the NQSAP-PCB with all of the boards from the first five builds. A fourth backplane was added to hold the new XY and Index Adder modules. This now leaves a module slot empty - another opportunity!

The Arduino Loader is not active and the system is running a simple program that counts and saves and restores values from the stack.