Re: 8250LP - fault, how to fix?

From: Ethan Dicks (
Date: 2002-02-13 16:41:37

--- Adrian Vickers <> wrote:

> > > According to the FAQ, this means:
> > >
> > > "Zero Page - 6530, K3, 6504, H3"
> Indeed. Does "Zero Page" mean the drive is unable to retrieve data from the 
> chip, or it's all coming back as zeros, or something else entirely, do you 
> think?

"Zero Page" in the 6502 world means the addresses from $0000 to $00FF - the
"zeroth" 256-byte page of memory.  It's special because the 6502 (and family)
processors have instructions that know that the top byte of the address is
going to be zero, so you can leave it out...


    LDA $02
    LDA $0002

are not the same instructions or number of bytes ($A5 $02 vs $AD $00 $02)

The error from the disk drive is that the RAM between $0000 and $00FF failed
a RAM test.  In most Commodore floppy drives, that RAM is contained in the
6530 (along with other stuff).  In the D9060 and D9090 drives, there isn't
a 6530 - the zero page RAM is in a Motorola 6810 chip (128 bytes).

Ruud... don't pitch those defective 6530s... if it's just the RAM, it might
be possible to build a board that fits in the 6530 socket that has a
defective 6530 and an SRAM chip to "fill in" for the defective RAM.  It's
not a general solution as a board that completely emulates a 6530, but
I suspect it would be easier to make (not having to provide I/O...)


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