6502 NOP tester (was Re: New and reading the mail)

From: Ethan Dicks <erd_6502_at_yahoo.com>
Date: Tue Jan 7 14:19:00 2003

--- Cameron Kaiser <spectre_at_stockholm.ptloma.edu> wrote:
I wrote:
> > You can also build a NOP generator (use a second CPU chip) by bending
> > the appropriate data bus leads up and hardwiring the databus to the
> > NOP instruction (0xEA?) - You can then use a logic analyzer to monitor
> > the address bus for stuck bits and the select lines on the MSI chips
> > to see that they respond at the appropriate times.
> Hey, that's pretty slick! Yes, $ea is NOP on the 6502.

Thanks. I wasn't home and that was from memory.

I have one or two of these in a parts drawer that I bought from
the local C= dealer when they went out of business. *rummage*
*rummage* Here they are!

Pins 29, 31 and 33 are bent up and connected to pin 21, and pins
26, 27, 28 30 and 32 are bent up and connected to pin 8.

I recommend mounting the results in a machined-pin socket. One of
the two I have here has pin 1 broken off, no doubt from too many
rough deployments.

I also recommend not using one in an Apple II or any design where
*reading* memory locations can cause interesting side effects.
In Commodore hardware, you have to *write* to I/O registers to
make stuff happen; not so with the Apple.


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Received on Tue Jan 07 2003 - 14:19:00 GMT

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