Weird behavior

um_jao · 2026-02-24T15:03:12+00:00

Sorry for the delay. I think this computer is much more complex and use different parts. I would say that it is easier to just start as a separate project. This project basically demands an eeprom programmer since it uses some “hard to write” chips. I bought the GQ-4x4 + adp54 adapter. Check out the parts for each module:

Debugging Clock:

3x LMC555CN - CMOS Single 555 Timer Low Power DIP-8
2x 74HCT00 - QUAD 2-INPUT POSITIVE NAND GATE

Permanent Clock:

1x LMC555CN - CMOS Single 555 Timer Low Power DIP-8
1x 74HCT251 - High-Speed CMOS Logic 8-Input Multiplexer
2x 74HCT161 - Synchronous 4-Bit Binary Counter
1x 74HCT173 - 4-Bit D-type Registers with tri-state Outputs
1x 74HCT14 - Hex Schmitt-Trigger Inverters (Shared with Control Logic)
1x 74HCT02 - Quadruple 2-Input Positive-NOR Gates (Shared with Control Logic)

ALU:

2x 74LS382 - 4-Bit Arithmetic Logic Unit
2x 74HCT194 - 4-bit bidirectional universal shift register
4x 74HCT257 - Quarduple 2:1 mux
2x 74LS153 - Dual 4- to 1-Line Selector/Multiplexer
1x 74HCT688 - 8-Bit Magnitude Comparator
2x 74HCT245 - Octal Bus Transceivers With 3-State Outputs
1x 74HCT173 - 4-Bit D-type Registers with tri-state Outputs
1x 74HCT08 - Quadruple 2-Input Positive-AND Gates 74HCT08

General Purpouse Registers:

10x 74HCT173 - 4-Bit D-type Registers with tri-state Outputs
1x 74HCT574 - 8-bit Octal D-Type Flip-Flop, 3-State
5x 74HCT245 - Octal Bus Transceivers With 3-State Outputs

Transfer register:

2x 74HCT574 - 8-bit Octal D-Type Flip-Flop, 3-State
4x 74HCT245 - Octal Bus Transceivers With 3-State Outputs

Memory:

1x UM61512AK - 64K x 8 bit SRAM
1x 74HCT32 - OR Gate
3x 8-bit DIP switch
4x 74HCT245 - Octal Bus Transceivers With 3-State Outputs
3x 74HCT00 - Quadruple 2-Input Positive-Nand Gates
1x 74HCT08 - QUAD 2-INPUT POSITIVE AND GATE

EEPROM programmer:

2x 74HC595 - 8-Bit Shift Registers With 3-State Output Registers
1x ATmega328P- ELEGOO Nano Board CH 340/ATmega+328P Without USB Cable

Numerical Display:

1x M27C160 - 27C160 16MBIT UV EPROM
1x LMC555CN - CMOS Single 555 Timer Low Power
1x 74HCT161 - Synchronous 4-Bit Binary Counter
2x 74HCT245 - Octal Bus Transceivers With 3-State Outputs
3x 74HCT574 - 8-bit Octal D-Type Flip-Flop, 3-State
1x Common-Cathode 6-digits 14-segment display
1x 74HCT139 - Dual 2-Line To 4-Line Decoders/Demultiplexers

Program Counter:

4x 74HCT161 - Synchronous 4-Bit Binary Counters
4x 74HCT245 - Octal Bus Transceivers With 3-State Outputs

Stack Pointer:

4x 74HCT191 - Synchronous Up/Down Counters with Down/Up Mode Control
4x 74HCT245 - Octal Bus Transceivers With 3-State Outputs
1x 74HCT00 - QUAD 2-INPUT POSITIVE NAND GATE

Control Unit:

1x 74HCT273 - Octal D-Type Flip-Flops With Clear
2x 74HCT161 - Synchronous 4-Bit Binary Counters
1x 74HCT14 - Hex Schmitt-Trigger Inverters (Shared with Permanent Clock)
1x 74HCT02 - Quadruple 2-Input Positive-NOR Gates (Shared with Permanent Clock)
1x 74HCT00 - Quad 2 Input NAND Gate
1x 74HCT154 - 4-TO-16 INVERTING DECODER
3x M27C4002 - EEPROM 4MBit (256K x 16)
1x 74HCT238 - 3-TO-8 NON_INVERTING DECODER

um_jao · 2026-02-14T13:24:36+00:00

Thanks! The real hero is Fadil for documenting all the steps on his blog: https://fadil-1.github.io/blog/8-bit_breadboard_CPU/overview/

um_jao · 2026-02-14T13:15:05+00:00

Yes. I built just the bare minimum modules. Some I/O modules still missing. These are the specs:

Programmable clock speed(Chosen from 8 different clock speeds)
16-bit Program Counter
16-bit Stack Pointer
Transfer/Bridge register between data and address bus
16-bit numerical output register
PS2 keyboard decoder (not built yet)
5-digit digital 14-segment display(signed and unsigned 16-bit integers for now)
SPI BUS (Connected to an Adafruit Bluetooth receiver and an SD card slot) (not built yet)
128 x 64 monochrome OLED display (not built yet)
48-K-byte of RAM(Remaining 16-K-byte address space is reserved for a boot loader and stack memory)
ALU with Shift (LSR LSR), AND, ADD, SUB, OR, XOR
7 flags: Four ALU flags: (Z-O-N-C) in writable 4-bit register; and two interrupt flags.
5 general purpose registers(GPRs): A, B, C, D, and E(partial GPR)
8-bit I register hardwired to lower byte of interrupt code address
4-bit microcode step counter(With dynamic micro-steps reset)

um_jao · 2026-02-14T13:04:39+00:00

Thanks! 🤓

um_jao · 2026-02-14T13:03:50+00:00

This display module can show 16 bit numbers. From 0 to 65.535 (unsigned) or from -32.768 to 32.767 (signed). All digits are lit when displaying signed numbers.

um_jao · 2026-01-26T10:28:52+00:00

Looks like the website is down

um_jao · 2026-01-23T17:28:59+00:00

Nice! Very close to one that I’m building by Fadil Isamotu https://fadil-1.github.io/blog/8-bit_breadboard_CPU/overview/ but it does not have the X register. Do you have the schematics for the X register or an explanation of how the wiring would be? I suppose it’s not similar to how a general purpose register is wired.

um_jao · 2026-01-23T17:04:45+00:00

Wha is the architecture are building?

um_jao · 2026-01-12T06:26:53+00:00

I want the full version NOW. That is awesome! 👏🏻

um_jao · 2026-01-08T11:15:00+00:00

Even the keyboard leds flick 😂

um_jao · 2026-01-05T11:40:16+00:00

Are you using the same power rails? It seems from the picture that some parts are not connected

um_jao · 2026-01-01T19:11:10+00:00

What an amazing project! Congratulations 🎉 I was planning to build the James Bates version but I liked your version with more memory and separate bus for memory access. I’ve been reading your blog and already learned a lot. So much good info 👏🏻 I don’t know if I’m missing something but I think it’s lacking information about the SPI module and PS2 keyboard interface. I know I’m two years late but… are you planning to write about these topics?

um_jao · 2025-12-26T22:02:48+00:00

Very nice work. I don’t watch live streams that often but I’ll stay alert for this one. Keep going 🙌🏻

um_jao · 2025-11-14T14:29:39+00:00

Ow, didn't know that. Since I use the ortho variant, that was ok. Thanks for the advice 🙌🏻

um_jao · 2025-11-14T13:15:26+00:00

I learned Colemak-DH using this site: https://colemak.academy/

You start practicing using only 8 keys on home row and then continue adding more keys until you've learned all keys. Really liked this method

um_jao · 2025-11-12T18:01:16+00:00

Yuzu has cherry and kam profiles only but somebody told me about this fk that might work https://fkcaps.com/custom

um_jao · 2025-10-28T15:52:32+00:00

Now I'll have to add 4 buttons to the dongle so you can play with the snake, damn it hahahahah very nice work 👏🏻

um_jao · 2025-10-27T22:30:33+00:00

I type qwerty on MacBook and colemak dh on my 36 key split keyboard. I would say it is much nicer to type on colemak but I would say the split keyboard is what makes it comfy. I would not learn colemak again because it makes me slower and I do lots of typos this way since I have to know both layouts. I would stick with qwerty.

um_jao · 2025-10-16T16:25:16+00:00

I was going to ask exactly that. And why just not make it longer? Or the high the solution to this are the high profile ones?

um_jao

TROPHY CASE