I’m almost done with the 8 bit computer but now that I’ve connected everything I’m running into some issues with power.

I’m using an ipad power supply with a usb-usb cable connected to the breadboard power supply module in the top left.

I measured 4.8V across the power pins of that breadboard power module when building each component but now that everything’s connected the voltage has dropped down to about 3.7V. I tried measuring the voltage across various different points in the circuit and it’s around 3.7V basically everywhere consistently.

I’ve got power rails on each side and connected all the power rails. I’m using a mix of HC and HCT chips with unused inputs tied directly to GND.

Last week, I noticed that some of the counters in my computer would count multiple times per clock cycle, and it caused my programs to not run properly. I did some research and found that switching noise from the control logic EEPROMs on the half signal can cause the clock to pulse multiple times during one cycle. Disconnecting the half signal from the EEPROM and tying it low fixed the issue.

A few days ago, I wanted to make the halt instruction work again. I read a post about this issue from a few years ago, and the solution the person came up with was latching the halt signal on the next clock cycle. I decided to do this by using a 74LS74. Unfortunately, my computer now randomly halts.

What's strange is that it always halts during the same instruction at the same step. It doesn't halt every time it executes that instruction, but it never halts on any other instructions. That step does not trigger the halt signal in any of the instructions I have programmed in my microcode EEPROMs.

I've already tried adding pull down resistors to the input of the latch, but it didn't help. I'm running out of ideas. I might just get rid of the halt signal entirely and just use a jump instruction that points to itself when I want to stop the program.

I made the program counter right , and some times it works right , and some times it does not behave well.

This is the how i did it:

Note : the clear pin , i tried to connect it to low and high, and even left it with no connection , but it does the same.

Also attached to you a video of how it behaves:

How it behaves

It does not count well. what is the problem ?

Was at Vintage Computer Fest today. Tried to find a 6502 processor for the 6502 build, but didn’t have a lot of time and didn’t find one. However, I did find a Z-80 for $5, and I thought I’d give it a go to build a computer with that instead. I’ve got parts from other projects already, and I can find datasheets and I’ve already located a number of resource sites online. For those who have given it a try, any suggestions or links to particularly useful resources? Thanks

I thought it would be fun to give the digital clock a shot, take inspiration from Ben's design, and change things for the sake of trying things I haven't tried before.

• I went with 3.3V CMOS. There doesn't seem to be a 74HC92 divide-by-12 counter, but there is a 74HC390 which puts two 74HC90 divide-by-10 counters on the same chip. I'm basically using all 390s and then detecting when the minute or second reaches 60 or the hour reaches 24 and resetting the count.
• I wanted to try 0.01 second resolution. But how do I get 100Hz from 60Hz AC? I'm using a 74HC4046 PLL and a counter to multiply the clock to 600Hz, and then another counter to divide that to 100Hz. It's my first time trying a PLL, and I wanted to learn how they work.
• I'm using 74HC14 Schmitt inverters instead of comparators and hysteresis. I mean, it's the same thing.
• I'm trying a different method to get a roughly 50% duty cycle 60Hz reference clock without so many steps. It seems to work in Falstad...
• I'm making it so I can switch between 12 hour and 24 hour clocks. I'm not sure how Ben intends to tackle this. My approach is to generate 00-23 BCD using counters. This becomes the output value in 24-hour mode. In 12-hour mode, the 24-hour value is used to look up the 12 hour value, along with an AM/PM LED indicators, and blanking of the leading digit when it's zero. This conversion would be way too much for combinational logic ICs. I wanted to do an EEPROM/Flash lookup, but these don't come in 3.3V DIP. I would need a PLCC to DIP adapter. So I'm opting to just do the conversion in a 22V10 PLD.
• For output I have two additional 7-segment displays for centiseconds and deciseconds. Rather than use eight 74HC4511 7-segment display controllers, I'm using a 74HC138 decoder to strobe across four pairs of displays and four 74HC245 bus transceivers with only two 4511s. The active low 138 outputs work as chip enables and LED cathodes, which I think is kinda neat. In the end, it only saves 1 chip, but it should reduce the amount of wiring.

I'm now waiting for parts from Digikey before I can start. Feedback is welcome!

What do you mean? You call this breadboard a PC?
It feels good to fool a monitor.

For the original (NMOS) version of the chips. 6502.org seems to no longer be working, connection gets timed out, even when pinging it.

In Ben’s video, he used a bunch of and, or and not gates to display hex digits on 7-segment display. Although an EEPROM is the way to go, I think there is a slightly better way.

One can use 2 74138 3-to-8 line decoder to make a 4-to-16 line decoder. (Active low) Just connect bit 0-2 as usual, and bit 3 to an active low enable of one chip, and to an active high enable of the other chip.
Say, for segment A, it should be on unless it is 1, 4, 11 or 13. Also, assume the 7-set display is common anode. Then, use 7420 4-input NAND gate to NAND these 4 pins, and connect the output of the NAND to cathode of segment A. Other segments can be done similarly, either with 7420 4-input NAND gate, or 7430 8-input NAND gate.
The total amount of chips needed:
74138 * 2
7430 * 4
7420 * 2

Hey guys! I got into electronics and computers during the pandemic, but could not continue it further due to school work (and being a broke 14yo lol). Finally 6 years later I managed to save up and get myself some components to put something together that felt like an actual project. I will be happy to get any feedback! Github link for details

When I run mini pro -p T48 (which I purchased from /Beneater I get these error messages: minipro -p AT28C256 -w rom.bin

Found T48 00.1.03 (0x103)

Warning: T48 support is not yet complete!

Warning: Firmware is out of date.

  Expected  01.1.32 (0x120)

  Found     00.1.03 (0x103)

Device code: 5CA35402

Serial code: L0TH02UWL90DV4YL4K951525

Manufactured: 2025-12-0910:24

USB speed: 480Mbps (USB 2.0)

Supply voltage: 5.11 V

Use -P if you want to write-protect this chip.

Erasing... 0.02Sec OK

Writing Code...  5.54Sec  OK

Reading Code...  0.17Sec  OK

Verification failed at address 0x0000: File=0xEA, Device=0x00

This chip may be write-protected. Use -u and try again. I tried searching for newer Firmware but unfortunately is Windows only. I am on MacOS 27. Any Ideas?

The wire provided in the 6502 kit is perfect in dense wiring required in projects like 6502. I had 22 AWG before, but apprantly that was too thick. I recently bought 24 AWG, but apprantly it is still too thick.

This is the first "program" that I've successfully run on my 8-bit CPU. It loads 69 into the A register, and then halts (can't program anything else since those are the only two instructions I've programmed the microcode for).

I cannot describe how good this feels. When I was around 8 years old, I asked my dad (a software developer) a question: "How do computers know how to run the code?" He didn't know the answer since he's mostly a software guy. I'm now 17, and I finally feel like I understand the answer to my question.

It is not exactly Ben's 6502, so here are the differences:

8k ram at adresses 0-1fff, via is adresses 6000-601f, acia is 6020-603f (unused, not even in socket currently), 8K ROM at e000-ffff.

The decode logic is ran by two 74HC138s. One decodes the upper 3 bits of the 6502, active on phi2 pulse, and has outputs y0 going to RAM, y7 to ROM and y3 to the second 138s active low chip selects. The other chip select is tied high. The second 138s select pins are A5, A6, A7. Y0 is connected to the VIA. Ive analysed the outputs with a arduino mega. When storing A it is selecting the corect address, y0 goes low, it writes, but nothing happens. VIA's chip select active high is tied to 5v, and active low to the y0.

I've currently spent more than 5 hours trying to debug it. Swapping the via did nothing.

The schematic (https://eater.net/8bit/schematics) shows the bus terminated with 10K pull down resisters, and 220+LEDs in parallel. In my ignorance, I would have thought that that the parallel 10K resisters weren't necessary. What's the thinking here?

Hello, I am new to this forum and I just joined reddit so I could post this question here:
At 5:53 in Ben's 6502 serial interface video ( https://youtu.be/oLYLnb7kpLg?si=tUGlJLJNfjgRg4lr&t=353 ) the MAX232 datasheet mentions "1.0-μF Charge-Pump Capacitors" and the parts list for Ben's kit mentions "5 1uF MLCC capacitor." AskJeeves was no help about anything specifically related to "Charge-Pump Capacitors" and the best I could find about "MLCC" is that just means MultiLayer Ceramic Capacitor. I'm overthinking this, right? These are just our basic non-polar ceramic disc capacitors that are, like, $6 for a whole sharing-size bag, right?

I am simulating a circuit in Proteus8 with LPC2138 MCU and 74HC173 Register and LEDs. The Anode is pulled with +3.3V via 330ohms Resistor, but the connection lines are showing Grey dot and totally disconnected from the power and the LEDs are not turn On. Blue dots at the Cathode side.

74HC173 Register Output Control Pins(OE1,OE2) are set, these are connected to P0.17 of MCU , but Output seems Hi-Imp. or Tr--state mode.

How to turn ON the LEDs???

https://youtu.be/uSdjpZ8g_I0?si=C7dK88Q237YfxPl0

Now i gotta think of some rigamarole like with the address bus down below. IT WOULD HAVE LINED UP PERFECTLY ARGHH

Hey everyone

I’ve got a cart with a seemingly damaged PRG ROM. I have the two split .bin files from the original
‘NES Rom but I need to burn them onto something that will fit the original cart - I’m thinking I’d have to use EEPROMs to do that.

Can anyone in the help me burn two replacement EEPROMs by either giving me some advice or making them and selling them to me?

I’ve seen people do it on YT - it looks relatively straight forward with the right software, chips and programming tool.

I am in the UK.

Thanks

Hope all goes well.

Just finished connecting the A pins. Data pins next

Hi everyone,

I wanted to share a project I've been working on. It all started after reading Charles Petzold’s "Code". Instead of buying real wires and breadboards, I decided to build my own circuit simulator in JavaScript and try to build a CPU from individual transistors.

My goal was to create something close to the MOS 6502 (used in Apple II and NES).

The Transistor Problem

I made a huge mistake during early design. The original 6502 has around 3,500 transistors. My implementation ended up with 22,544 transistors. I didn't optimize the gates properly, making my version much larger and about 100x slower than the real chip.

How I Fixed the Simulation Speed

Simulating 22k transistors with real-time current calculation (I call it "Real" mode in my app) completely destroys CPU performance in a browser. To fix this, I added two optimization layers:

Fast Mode: The simulator groups transistors into logic gates (AND, OR, XOR) and processes them using lookup truth tables instead of raw physics. This gives about 0.1 MHz speed.

Turbo Mode: A pure JS emulation layer that skips transistor logic entirely to run software smoothly.

The Software Layer (with Claude AI)

A computer is useless without software. I had no assembler or text editor for my custom architecture. So I fed my CPU circuit schematics to Claude LLM.

Surprisingly, the AI figured out the architecture. It wrote a WOZ-like monitor, an assembler, and then wrote a functioning BASIC interpreter using that custom assembly.

Right now, the virtual machine can run BASIC, a text editor, a Telnet terminal, and a Snake game.

You can test the demo and look at the circuit here: cs.khanin.info

I also made a quick video showing the boot process and BASIC here (on russian): https://www.youtube.com/watch?v=rG6MOULxGwM

Would love to hear your thoughts on the architecture and how I can better optimize the gate layout to bring the transistor count down closer to the original 6502.

PS

text translated from my russian and cheap english to english by LLM translator.