Did you perchance forget to terminate SOB (pin 38) on the 65C02? Your “schematic” shows that it is floating, which is a no-no on almost all CMOS devices. Unless you plan to use SOB for something, you need to pull it up to V CC .

You are right I forgot to pull that high.

The reason for me ...

Hi everyone it has been a while. I have updated the schematics of my computer. And ordered pcb's but unfortunately my computer does not work.
When I push the reset button I don't get what I expect I used Ben Eaters Arduino program to debug the output. I expect to see the reset vector (fffc, fffd ...

I just found a 74HC86 so I replaced the 74HCT86 with this 74HC86 but it does not make much difference. I need to press the button multiple times to toggle the caps lock function. Do I need some debouncing of the switch?

If you *are* using a 74HC86 (as shown in your diagram), then here's the next troubleshooting step I'd suggest.

With the circuit powered up (and without pushing the pushbutton), add a temporary connection so that the input of the first "inverter" (pin 1 of the '86) connects to 0 volts (ground). Use ...

Obviously here you've used an XOR gate for U1C so that if shift lock is enabled, shift will return to lower case; if either shift or shift lock is active, the output is 'shift', so that's fair enough.

Assuming a shift lock hasn't happened yet, the output of U1B is low, so it's holding the input of ...

I found some time to build a new version of my keyboard prototype and the keyboard matrix works now. I did not add anything jet to stop the clock signal getting to the counters. I will see what happens now I fixed some issues. I still have a problem with the caps lock feature. I added a pull down ...

I came up with a simple solution. What if I add two NAND gates to stop the clock if the strobe is high.
One to invert the strobe signal and the other one with the result of the inverted strobe and the clock signal.
I'm not sure if this will work in practice but in theory it does.
You'll ...

I came up with a simple solution. What if I add two NAND gates to stop the clock if the strobe is high.
One to invert the strobe signal and the other one with the result of the inverted strobe and the clock signal.
I'm not sure if this will work in practice but in theory it does.
You'll ...

I came up with a simple solution. What if I add two NAND gates to stop the clock if the strobe is high.
One to invert the strobe signal and the other one with the result of the inverted strobe and the clock signal.
I'm not sure if this will work in practice but in theory it does.

Hi everyone,

I made a simple prototype of the keyboard to be able to test it. This is my first ever PCB :P.
Of course I made some mistakes so I added some patches.
The shift key did not have a pull-down resitor so I added it and the 7493 counters weren't cascaded so I had to cut a trace and add a ...

What if I use a 74132 Quad Schmitt Trigger NAND Gate instead (a NAND gate could be used as an inverter). Would this work as well? I can just use this single 74132 chip to replace the 7414 and the 7400 chips.
That's what's in the whole-computer schematic at the top of the "circuit potpourri" page ...

The VIA register select inputs are connected to signals A0-3 while all others seem to be connected to Addr0-3.

Also, the (modern) VIA's /IRQ output is totem pole. Connecting them together may result in short circuits through the chips. You need to add a diode to each VIA /IRQ output so the VIAs ...

I finally found some time to play around a bit. I created a breadboard with a shift and a caps lock button. I already use a 7486 IC (quad xor gate) to determine if the shift output should be high or low based on the shift and caps lock buttons. So I decided to remove the hex inverter IC and use 2 ...

The VIA register select inputs are connected to signals A0-3 while all others seem to be connected to Addr0-3.

Also, the (modern) VIA's /IRQ output is totem pole. Connecting them together may result in short circuits through the chips. You need to add a diode to each VIA /IRQ output so the VIAs ...

It has been a while. I found some time to do some work on my computer. We havent talked about my computer so far only about the keyboard. I designed a schematic of the computer I want to build. I said that I want to add game controllers, video and sound outputs to my computer but I think it would be ...