Re: More detail... Help with copying D64 files to Disk

From: Anders Carlsson <>
Date: Tue, 3 Nov 2009 14:03:10 +0100
Message-ID: <00dd01ca5c85$fe8a6950$>
Scott wrote:

> Now that I've got a working 64C, what would you recommend changing in the 
> defected 64C. the Processor (6510), PLA or both?

Ray Carlsen writes:

"Unlike the one in the C64, the PLA in the C64C runs cool to the touch. I've 
never seen a bad one. Of course new and old versions are not 
interchangeable. The older 6510 MPU seems to work in the C64C as a sub for 
the 8500. I have tried an 8500 in an old C64 and it worked (diagnostic test 
only), but I don't know how well these chips interchange in actual use. All 
of the 8500 series chips run cooler than the older 6500 series."

It seems remarkable if the 906114-01 (82S100) PLA in the breadbox C64 very 
often breaks but the 251715-01 (LH5062B, YM3535) PLA in the newer C64C 
almost never breaks.

It should be fairly easy to construct a test program which swaps Basic, 
Kernal and Char ROMs in/out and see exactly what causes the machine to 
crash. This program should be written in machine code, possibly entered as 
DATA statements:

LDA $01
AND #$FE ; disable Basic ROM
STA $01
INC $D020
LDA #$37 ; default value
STA $01

10 DATA 120,165,1,41,254,133,1,238,32,208,169,55,133,1,88,96,-1
20 I=679
40 SYS 679

To disable Kernal, I suppose you replace 254 by 253. To switch in Character 
ROM you replace 41,254 by 9,2 (ORA #$02). Please correct me if I made any 
mistake here.

I don't know if there is any need to check the data direction register at 
$0000, would programs often change it?

Good luck!

Anders Carlsson

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Received on 2009-11-03 14:00:04

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