Re: 1541IDE and 1541IDE-S

From: Jim Brain (
Date: 2007-12-12 16:50:25 wrote:
> Pure curiousity: why didn't you use the SCH I sent you as base?
> For every one else:
Given the additional complexity of the device, I was afraid that it was 
not exactly a superset of the 8 bit interface.  As well, I was afraid 
that by deleting things from the 16 bit design, I would render the 8-bit 
idea useless.  My task, as I saw it, was to layout the 8 bit interface, 
and I wanted to make sure I got that done.  Finally, the 16 bit design 
uses more ICs.  The 8 bit design was vary frugal with ICs, and I felt 
that was an elegant design on your part.  However, now that I know they 
are equivalent, I can try to lay it out minus the RAM, ROM, etc.
> Sorry to say, but this is a very bad idea IMO. At this moment I store several parameters, like the size of the disk, the start of the directory and the link to the next sector, as four bytes in a row. Copying them to disk can be done like this:
>   ldx #3
> 1 lda LBA0,X
>   sta IDE_reg,X
>   dex
>   bpl 1
> With a shifted address a more complex routine is needed.
> That's why I used this scheme:
> A0..3 : basic IDE registers
> A4    : choosing CS0 or CS1
> A5    : high/low byte
> When I started with the 8 bit design, I could use a lot of the original 16-bits sources as I only had to drop everything conneted with A5. 
You are correct, of course, and it's trivial to change it.  However, it 
does make the memory map funky:

$00-$1f=IDE registers low byte
$20-$3f=IDE registers hi byte

Unless someone objects, I will make the change.  That will indeed make 
it 100% compatible with your original design.

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