[Coco] [Color Computer] Floppy contoler Q

[Arthur Flexser]

If you select DS3 without selecting another drive bit, then the fourth drive is
selected.  Without hardware modifications, only 3 drives can be used as
double-sided.


On Sun, 15 Jan 2006, 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. 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.
> 
> 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).
> 
> Cheers.
> 
> Phill.
> 
> 
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