[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
People having trouble with vz bouncing email to me should add the word
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