The WR\ to the memory needs to be separate from the signal to the VIA. Make sure you're observing that. The VIA needs the RS and R/W lines to be valid and stable before the rise of phase 2. I have never seen a VIA come defective when new, even though we used them for 13 years in one of our products ...

I know that it is unusual and can be complicated, I had my reasons for that and still have to implement these reasons

will have a look at that later,

for now I switched the WDC 65C22S for a Rockwell R65C22P and added a pullup-resistor at the /IRQ-Pin, now it works flawlessly, even at higher clockrate

and thanks Wilson for the primer, should've read it more thorough before designing the pcb ^^

ok, found something out... after back-checking with the 6502-primer here I noticed that /WE should be qualified by Phi2, so that on Phi2=low no write operation would be possible...
I hacked together a small logic circuit out of 2 NAND gates which are first inverting R/W from the 6502 and then ...

then again, why did the manual approach work?

on my own SBC I posted a while back (didn't have much time since then but now I'm tackling it again), see http://forum.6502.org/viewtopic.php?f=12&t=6513

I also tried to do something different. basically I tried to RTI to a specific address with the following:


lda #$80
pha
lda #$20
pha
php
rti ...

Hey everyone,

I'm currently at a loss.... I try to test and play with interrupts, which btw work as intended, but the RTI instruction is behaving strange...

As soon as I try to RTI, the processor is reading the wrong return address and just randomly jumps anywhere... I logged it and at Interrupt ...

I am every curious about your memory layout and banking, as I am exploring similar issues. I've considered (very briefly) the consequences of swapping bottom RAM including the stack, and decided it's best to avoid doing so, if at all possible.
well, I decided to just try it... in worst-case, I'll ...

This looks really cool! Hoping I can get mine to this point one day. Where do you get that eeprom holder and does it allow you to program it without removing it from the board?

sorry for the late response...

these sockets are called ZIF (Zero Insertion Force) and are there to easily be able to ...

working in an electronics company I have seen things only god knows what happened there....

one client specified a schematic and the exact BOM, we made the PCBs accordingly to the BOM and schematic, ordered a prototype and found out they specified smaller parts than they were intended to use. I'm ...

@jfoucher
as I said, I had these chips lying around and finally wanted to do something with them. I did a lot of dumpster diving once and found these in nearly pristine condition...
I know I already have more IOs than I ever need, but I like to think a bit easier here... PIA ist just output for me ...

So far I'm just writing libraries and test-codes. PIA library and VIA library (mostly just initializations, timers will come soon) are working as well as a library for the 2x16 character lcd in 4bit mode. I have a connector for a 4x40 char LCD as well, but this is essentially 2 seperate displays in ...

Hey everyone!

I'm currently designing/testing my own 65C02 computer (inspired by Ben Eater) and thought I might post it here.
I wanted something versatile and fun to play with while learning assembly language and the 6502 seemed a good choice becuase of its already big community.

I put a lot of ...