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Build An 8-Bit Computer by Ben Eater (Part 4) - Output Register and CPU Control Logic

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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.

Kit Includes:

Part No.
Qty.
Description
149948
1
Switch Push Button Tactile SPST OFF-(ON) 15 VDC @ 20mA Actuator Height 0.13 Inch
151116
5
Capacitor Ceramic Disc 0.1µF 25V ±20%
15229
5
Ceramic Disc Capacitor 0.01µF 50V ±20% Z5U
2299511
4
Red Single-Digit 7-Segment LED Display 0.5"H
2234071
20
LED Blue Diffused 5mm T-1 3/4 470nm 350mcd
2258831
1
3-Pin SPDT Slide Switch
2283767
6
830 Point Solderless Plug-in Breadboard with 4 Power Rails 21-26AWG ABS
27422
1
IC LM555P Single Timer (LM555CN,NE555N,TL555P,MC1455P)
333973
20
LED Red Diffused 5mm (T-1 3/4) 643nm 75mcd 36VA
46252
1
IC 74LS00 Quad 2-Input Positive NAND Gate DIP-14
46287
1
IC 74LS02 QUAD 2-INPUT POSITIVE NOR GATE
46316
2
IC 74LS04 Hex Inverter
46375
2
IC 74LS08 Quad 2-Input Positive AND Gate
46412
1
IC 74LS107 Dual J-K Flip-Flop
46607
1
IC 74LS138 3-to-8 Line Decoder/Demultiplexer
46623
1
IC 74LS139 Dual 2-to-4 Decoder/Demultiplexer
46818
1
IC 74LS161 4-BIT Synchronous Binary Counter
46922
1
IC 74LS173 4-BIT D-Type Register 3-State Output
47386
1
IC 74LS273 Octal D-Type Flip-Flop
690700
40
Carbon Film Resistor 220 Ohm 1/4 Watt 5%
690865
5
Resistor Carbon Film 1k Ohm 1/4 Watt 5%
691104
10
Resistor Carbon Film 10k Ohm 1/4 Watt 5%
691340
5
Resistor Carbon Film 100k Ohm 1/4 Watt 5%
693901
10
LED Green Diffused 5mm (T-1 3/4) 565nm 12.5mcd 60VA
74691
3
IC 28C16A-25 EEPROM 16K-Bit 250ns CMOS Parallel
911189
2
IC 74HC595N 8-Bit Serial-in Serial or Parallel-Out Shift Register without Latches (Tri-State) DIP-16
2283855
1
Keyestudio Nano CH340 Development Board

Resources & Downloads

Output Register Videos


Designing a 7-Segment Hex Decoder


Using an EEPROM to Replace Combinational Logic


Build an Arduino EEPROM Programmer


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

Notes

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

Notes

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:


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Specification Value
Design LevelIntermediate Kit


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