Re: Hardware emulation of 6509 using 6502?

From: Jim Brain <brain_at_jbrain.com>
Date: Sun, 25 Feb 2018 14:01:40 -0600
Message-ID: <2b15e4d4-e409-a84b-fda5-80e3d5c5d0f0@jbrain.com>
Right now, even forgetting the PORT register, the 6502 is deviating from 
the 6509 in operation right after reset.

https://github.com/go4retro/Fake6509/blob/master/ref/6509%20versus%206502.pdf

Left side is 6509, right is 6502.

R/W, A0-15, D0-7,PHI2 are all bridged.

https://github.com/go4retro/Fake6509/blob/master/pcb/Fake6509_v2%20Schematic.pdf

PORT is set to output $f (15) as per datasheet.

The system goes along fine until the CMP $03fa at $f99e.  The 6509 reads 
$f0, while the 6502 reads $f8.  After a bit, the paths greatly diverge.  
I think I am out of my element, and need help to move beyond this.

Jim


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Received on 2018-02-25 21:03:45

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