6502.org

Hi all

Today I started assembly of my first 6502 machine today but having a bit of trouble getting it running.

So far it's simple: reset circuit working and generates a nice low pulse when the button is pressed. Phase 0, 1, 2 and SYNC signals all look right.

BUT! I've got the data bus fixed to $EA to force it into a NOP loop and nothing is happing. R/W is low, and so are all address lines.

I'm trying to see what could be causing this but all my connections appear right. Does the above point to anything obvious?

Is it a WDC cpu? They feature a BE (bus enable) pin which needs to be high. Sounds like maybe it's not.

Check the other "mystery pins" too, here on Garth's site.

That's exactly what it was, thank you!

I'm using a WDC chip, and my circuit was based on someone using an older MOS one.

A big thrill, I expect. Congratulations!!

Yep, it's only taken me about 4 years to get to this point!

You didn't ground pin 1 of the MPU, I hope. Pin 1 on non-WDC 65C02s is a ground, but is the VPB (vector pull) output on the WDC version.
The first step is always the hardest. Now that you have a working unit you'll find future builds easier to bring to life.

Good catch - I had this grounded! Bent the pin out from the socket as I was already using that handy pin to connect the decoupling cap.

Working on adding the RAM and decode logic, then will be ready for an actual program.