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

[Gene Heskett]

On Sunday 15 January 2006 00:40, Phill Harvey-Smith wrote:

>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 ?

>

Yup, if you're using the side select as drive 4, then it cannot be on 
when accessing the other 3 drives, hence they must be SS drives.


>> 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).


Interesting.  Have you looked at the Fujitsu MB8877.  Its supposed to be 
a cmos workalike to the 1793 from what I've read but that was years 
ago.  It was used in at least one coco controller, maybe two.


>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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-- 
Cheers, Gene
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