Weird data bus write problem Ben eater 6502

[CountChocula]

Hello! Really hard to tell what’s happening… does it do it consistently?

Just a super random idea, but maybe check the wiring for the A4 address line on your board to see if anything came loose… I wonder if perhaps it’s floating and the CPU ends up reading the data at $8018 instead of $8008–you’ll notice that the data at that address corresponds to what you’re seeing. Might be worth stepping a couple more times more to see what data shows up on the bus; that might give you a few more hints about what’s going on. Good luck!

[ojanhk]

Do not only check for loose connections, but if you have a multimeter, do a continuity check on the address lines between CPU and EEPROM. You might have swapped some address lines (like CPU-A3 going to EEPROM-A4 and vice versa).

[BigDumbDinosaur]

At what addresses is the 6522 mapped? How are you generating the 6522's chip selects? Not having a schematic for us to examine makes it quite difficult to offer much troubleshooting help.

That said, without RAM, your unit is extremely limited in what it can do. I suggest you add some RAM and be sure to have it visible in pages zero and one.

From where did you get your 6502 and 6522? What is the clock rate for your system?

[adrianhudson]

Is there any chance you could post the assembly rather than the dump if the ROM. I appreciate that you may not actually have an assembler but if you are following Ben's videos you should have access to a transcription - I'm pretty sure he makes them available.

EDIT: Forget that. I think CountChocula is on to something - check out the A4 connection. It seems to read a byte 16 (decimal) on from where it should.
BDD, the 6522 is mapped starting at $6000 on these boards.

[BigEd]

Welcome, feven! (Slightly odd that your head post here looks like a copy-paste of speculatrix's earlier thread. and you've used the same title for your new thread here.)