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

[Gene Heskett]

On Saturday 14 January 2006 23:25, Phill Harvey-Smith wrote:
>Hi,
>
>I'm just trying to claify the way the bits at $FF40 work on the RS-DOS
>cartrage, I have studied the circuit sheets for both the WD1773, and
>WD1793 based controlers but ams still unsure about bit 6, looking at
> the circuit sheet this appears to be wired to Pin 32 of the drive
> cable, which would be side select. This makes sense as the
> WD1773/WD1793 don't have a side select output, unlike the WD2797 used
> in DragonDos, which does. However a comment in the mess source says :
>
>/* An email from John Kowalski informed me that if the DS3 is
>* high, and one of the other drive bits is selected (DS0-DS2), then
> the * second side of DS0, DS1, or DS2 is selected.  If multiple bits
> are * selected in other situations, then both drives are selected,
> and any * read signals get yucky.
>*/
>
>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.

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.

>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).  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.

>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.

>Cheers.
>
>Phill.
>
Good luck Phill.

-- 
Cheers, Gene
People having trouble with vz bouncing email to me should add the word
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