Need a bit of help getting running

[Simon27]

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?

[Dr Jefyll]

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.

[Simon27]

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.

[Dr Jefyll]

Simon27 wrote:

Today I started assembly of my first 6502 machine

A big thrill, I expect. Congratulations!!

[Simon27]

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

[BigDumbDinosaur]

Simon27 wrote:

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

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.

Quote:

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

The first step is always the hardest. Now that you have a working unit you'll find future builds easier to bring to life.

[Simon27]

Quote:

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.

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.