2 layers191.1 × 114.3 mm
2 layers81.3 × 82.6 mm
Program Counter
DutchMaker/TTL-computer24Building a computer from scratch using 74xx logic chips
- Size
- 81.3 × 82.6 mm
- Copper layers
- 2
- Thickness
- 1.6 mm
- Parts
- 15
- Nets
- 85
- Pads
- 250
- Tracks, vias
- 788, 9
- Pours
- 1
- Routed
- Yes
- KiCad
- KiCad 5 (file 20171130)
- Created
- 11 Apr 2018
- Updated
- 4 May 2020
Overview
Program Counter is an open-source printed circuit board by DutchMaker, from the DutchMaker/TTL-computer repository on GitHub. It is a 2-layer board of 81.3 × 82.6 mm with 15 parts on 85 nets, routed with 788 tracks and 9 vias.
Its parts include 9 ICs and 2 connectors.
README
README.md74xx Computer
My attempt at building a computer from scratch with 74xxx logic chips.
Project Shelved!
I have abandoned this project, but only to reboot it with a different approach.
Make sure to check The DM-02 Computer which is my second attempt at a computer from scratch!
Status as of September 4th, 2019:
General architecture has been worked out as high level schematic.
Worked on instruction set, micro code, module documentation & general notes from time to time (see: Documentation). Only thing missing right now is some documentation on each of the modules.
The entire computer has been built in Logisim to verify that the way I had everything in mind is actually going to work.
I've built a microcode compiler for the Controller's ROM image. This takes a source file which defines all the microcode and compiles it into a binary image that is loaded into the microcode ROM.
The 74xx Computer's instruction set has been implemented, its assembly language is fully documented and I've built an assembler to convert assembly programs to machine code.
Circuit diagrams and PCBs have all been designed in KiCad and have been or are currently being produced:
- Clock (built and tested)
- Registers (built and tested)
- ALU (built and tested)
- Program Counter (built and tested)
- Stack Pointer (built and tested)
- Flags register (built and tested)
- Memory (built and tested)
- Memory Access Register (built and tested)
- Controller (redesigned circuit to account for reset ciruitry - waiting for PCB production)
- Main Board ( built and tested)
TODO's / Plans:
- Build the computer in real life (IN PROGRESS)
- First revision is based on separate PCBs that are all connected together by one large main PCB.
- If all works out, there may be a second revision will be one large PCB that contains all modules as one circuit.
- Write additional/updated documentation on all modules.
Parts
15| Qty | Value | Footprint | References |
|---|---|---|---|
| 4 | 74x191 | Package_DIP:DIP-16_W7.62mm | U2, U3, U4, U5 |
| 4 | 74x245 | Package_DIP:DIP-20_W7.62mm | U6, U7, U8, U9 |
| 2 | 470 | Resistor_THT:R_Array_SIP9 | RN1, RN2 |
| 2 | HDSP-4830_2 | Display:HDSP-4830 | BAR1, BAR2 |
| 1 | 74x02 | Package_DIP:DIP-14_W7.62mm | U1 |
| 1 | Conn_01x18_Male | Connector_PinHeader_2.54mm:PinHeader_1x18_P2.54mm_Vertical | J1 |
| 1 | MEMORY ADDRESS | Connector_PinHeader_2.54mm:PinHeader_1x16_P2.54mm_Vertical | J2 |
Questions
How big is the Program Counter PCB?
It measures 81.3 × 82.6 mm and has 2 copper layers, 1.6 mm thick.
What parts does the Program Counter use?
15 parts. The full list of its parts is on this page, with links to each part's symbol and footprint where PCBKit's library has them.
Where can I download the Program Counter KiCad files?
From the DutchMaker/TTL-computer repository on GitHub, at the commit this page was made from: the board is Circuits/KiCad/Program-Counter/Program-Counter.kicad_pcb. PCBKit opens the board in the browser, with nothing to install.
Can I use the Program Counter design in my own project?
Its repository states no licence, so its author keeps all rights: ask DutchMaker before reusing the design.
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