[Coco] Re: [Color Computer] Floppy contoler Q

[Phill Harvey-Smith]

Gene Heskett wrote:
> On Saturday 14 January 2006 23:25, Phill Harvey-Smith wrote:
>> This infers that this signal can also be used to select the 4th drive,
>> however I'm unsure of the way this could be done.
> 
> Yes, however, this is assuming all 4 drives are single sided.  Also the 
> drive might have to be programmed for motor on on selection.

So if you have 1..3 drives then Side select is exactly that ? But if you 
have 4 drives they have to be single sided ?

> It also required a jumper to be soldered onto the 4th drive to take it 
> to a valid drive select signal on the drive with the other 3 jumpers or 
> switches set open.

Yeah that makes sense.

>> It may be possible 
>> that the Tandy drives had some off board circuitry that somehowe did
>> this (or a non standard cable), since I have never actually seen one,
>> I do not know.
> 
> Their off board circuitry consisted of removing the connections from the 
> card edge connectors and twisting the cable such that for the first 2 
> drives, both were programmed to be (IIRC) drive 0 (unlike the pc drives 
> that were all drive 1).

But the same idea none the less, I use a similar twist (pins 10 & 12 
IIRC), to undo the bodge and let me use 2xPC 1.44s (as 720) on my 
CoCo/Dragon.

>			  It simplified things for the assemblers, but 
> made life difficult for us, so we usually installed, or soldered the 
> jumpers to assign the drive number on each drive, and then put fully 
> populated connectors on the drive cable.

Yeah that figures, in other words we use things the way they where 
designed, with a full cable and jumpers.

>> In case anyone wonders what I'm up to, I'm trying to port SuperDos (A
>> Dragon dos enhancement), to use the RS-Dos hardware, as I figure this
>> way an RS-Dos cartrage could be used with the Dragon (either the
>> British one or the Tano).
> 
> I'd suspect that using the 1773 chip in a rsdos controller might require 
> a software hack to superdos to compensate for the hard wired side 
> select signal in the shack & clones controllers.

And difference in read/write sector commands, IIRC the 1773/1793 encode 
the sector sizes slightly differently, and this affects the exact format 
of the command ($80 on rs, $88 on Dragon for read sec etc).

Yeah I have it disassembled, and am working on it that way with 
conditional assembly I can build for Dragon, Dragon Alpha/Professional & 
  hopefully RS-DOS. At the moment it seems to be reading sectors ok, 
just from the wrong side of the disk !

Phill.



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