Build An 8-Bit Computer by Ben Eater - Output Register and CPU Control Logic (Kit 4 of 4)
This kit is another two-part build, and the first part is the output register. The output register is similar to any other register (like the A and B registers) except rather than display its contents in binary on 8 LEDs, it displays its contents in decimal form on a 7-segment display. Doing that requires some complex logic, but luckily there's an easier way if you check out the output register videos below.
Before building the control logic, we want to connect all the modules to a shared bus and test things. The modularity of the design makes it easier to test each module by itself, so we won’t ever get to a point where we put it all together and nothing works. Videos are below.
CPU Control Logic build: The control logic is the heart of the CPU. It is what defines the opcodes the processor recognizes and what happens when it executes each instruction. There are many videos for the CPU control logic build below.
Build an 8-bit Decimal Display for Our 8-bit Computer
Control Logic Prep Videos
8-bit Computer Build: Connecting the Bus
8-bit CPU Control Signal Overview
Rather than soldering the LEDs for the bus together as shown in the videos, you can put them in an open space on the breadboard. There will be ample free space on the right side of the breadboard just below the instruction register. Here's how that looks:
CPU Control Logic Videos
8-bit CPU Control Logic (part 1)
8-bit CPU Control Logic (part 2)
8-bit CPU Control Logic (part 3)
8-bit CPU Reset Circuit & Power Supply Tips
Reprogramming CPU Microcode with an Arduino
Adding More Machine Language Instructions to the CPU
Making a Computer Turing Complete
CPU Flags Register
Conditional Jump Instructions
An alternative to soldering a USB cable for power is to use a DC wall plug (P/N: 2217772) with a screw terminal adapter (P/N: 2227209). If you bought Kit #1, P/N: 2286623, you already have these. To create a more robust connection as described in the video above about power supply tips, you can use multiple wires like this: