Re: 1541 with an "harddisk"

From: Martijn van Buul (
Date: 2000-08-31 13:59:18

I have more remarks on this (It is an interesting idea!), but that'll have
to wait a bit - I suppose Mr. Philips wants me to do something for him
too :) wrote:
> As you know, I succeeded in connecting a IDE-HD to a C64. The biggest
> problem was writing the file handling system. The huge amount of work
> involved was one of the reasons I stopped any further development. Another
> reason was that I discovered that there was a much easier way to connect an
> "harddisk" to the 1541 and the only needed hardware is a piece of cable, a 25 
> pins male D-connector and a PC (IMHO 386, maybe 286 will do). 


> My idea is to disconnect the above pins (except PB3) and to connect them to
> the LPT-port of an PC.
>             6522                          LPT
>       Name  Meaning     pin               name        pin
>       ----  -------     ---               ----------  ---
>       PA0                2                D0           2
>        .                                  .
>        .                                  .
>       PA7                9                D7           9

This will be a problem, since these lines are bidirectional. 286 and 386
printerports mostly don't have a bidirectional printerport. Ofcourse,
you can simulate this by multiplexing the available inputs, but I think
that you'll be running out of time then. (It seems quite time-critical to
me as it is right now anyway).


> By monitoring PB0 and PB1 the PC will know when "to change track". The real
> drive needs a lot of mSec so the PC can take its time to fill a block RAM
> (IMHO only 8KB) with the data of that track.

Remember that the track has to be "GCRed" too. (Or you should use something
like a G64 image from the start). But why doing it on the fly? Memory isn't
really an issue. Since there won't be any other program running, a complete
GCRed image should fit into memory without much problems. You could do
the GCRing (and other needed modifications of a D64 image) when the image
is attached. After that, the only thing needed when the track is being
changed is modifying a pointer (which can be as easy as loading a segment
register with a new value)

    Martijn van Buul - -
	 Geek code: G--  - Visit OuterSpace: 3333
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