[Coco] Floppy Disk Controllers (Was: Good news: my CoCo 3 is back to life!)

[Joel Ewy]

Ok, I located a datasheet for the Fujitsu MB8877A, and can confirm that
it has the same pinout as the WD-179x, except that where the WD part has
a 12V supply on pin 40, the Fujitsu part has pin 40 as NC.  So it is a
5V only, pin-compatible drop-in replacement.

However, when I looked at my 26-3029 controller, pin 2, which I believe
is supposed to be the +12V line, has no trace at all on the card edge
connector.  So (at least) my 3029 presumably could not be used with the
WD part, since it lacks a 12V supply on the PC board.  If there were any
3029s that did use the WD part, they must also have used a slightly
different PC board.

JCE

Joel Ewy wrote:
> Mark Marlette wrote:
>   
>> Joel,
>>
>> Not sure what a WD-1791 is but you are right I almost forgot!!!!!!!!
>>
>> james?
>>
>> Mark
>>
>>     
> Ok, look what comes up at the top of a Google search on sy6591: 
> http://five.pairlist.net/pipermail/coco/2004-March/005585.html
>
> It's an interesting read.
>
> So.  The SY6591 might not be pin compatible with the WD-1791 (though I
> don't think that's really confirmed by the above) and the Fujutsu
> MB8877A as you (Mark) and Marty Goodman suggest, is a 5V-only,
> pin-compatible replacement for a WD 5V + 12V chip.  If the latter is
> correct, then Mike Pepe and I were wrong in claiming that the 26-3022
> was the only disk controller that required 12V.  In that case, 26-3029
> units that shipped with the WD chip instead of the MB8877A would as well.
>
> And I didn't even get past the first Google hit.
>
> JCE
>   
>> Quoting Joel Ewy <jcewy at swbell.net>:
>>
>>     
>>> Mark Marlette wrote:
>>>       
>>>> Joel,
>>>>
>>>> MB8877A was a 5v drop in replacement for the +12v WD1793, otherwise
>>>> you would need a MPI for that device.
>>>>
>>>> SY6591...that is it...No datasheet on that one at Cloud-9's
>>>> repositiory... :(
>>>>
>>>> I knows there was a mod for the J&M to work on the CC3.
>>>>
>>>> Mark
>>>>
>>>>         
>>>     Well, the one I have I got second hand (in fact, it came to me in a
>>> hacked-up standard full-length black plastic drive controller case with
>>> a Hard Drive Specialist sticker which was about 1/3 torn off so somebody
>>> could get to the screw.  So it's possible that it was modified before it
>>> got to me.  But if so, it was a _very_ subtle modification, as I see no
>>> jumper wires soldered on anywhere, and all the solder joints on the back
>>> side look original.
>>>
>>> And just this morning I checked it out on a CoCo 3.  I used it to load
>>> up a saved Sockmaster hi-color picture, and it worked like a charm.
>>> Maybe the modification was for 2MHz operation.  I didn't check that out.
>>>
>>> As for a data sheet, I think the SY6591 may be a second source of the
>>> WD-1791.  I bet James Daggett could confirm or refute that...
>>>
>>> JCE
>>>       
>>>> Quoting Joel Ewy <jcewy at swbell.net>:
>>>>
>>>>         
>>>>> L. Curtis Boyle wrote:
>>>>>           
>>>>>> On Mon, 05 Mar 2007 08:31:49 -0600, Boisy Pitre
>>>>>> <boisy at boisypitre.com>
>>>>>> wrote:
>>>>>>
>>>>>>             
>>>>>>> Gents,
>>>>>>>
>>>>>>> Not to put too fine a point on it, but FD-500 controllers will also
>>>>>>> work at 5v.  I think it's a very older, specific model number of
>>>>>>> disk
>>>>>>> controller that requires 12v and hence, the MPI.
>>>>>>>
>>>>>>> Boisy
>>>>>>>
>>>>>>>               
>>>>>> The very old, full size controllers that came with original full
>>>>>> height, really long grey 35 track single sided drives were the 12V
>>>>>> controllers.
>>>>>>             
>>>>> FWIW, I have a 26-3029, a 26-3129, a J&M (says JFD-COCO rev.A on the
>>>>> PCB), a Disto Super Controller, and a couple Super Controller IIs. 
>>>>> They
>>>>> all work on the CoCo 3 without an MPI.  (And none of them are an
>>>>> FD-501
>>>>> :) )  My 3029 has an MB8877 FDC with a WD9216 data separator.  The
>>>>> controller in the J&M is an SY6591.  All the rest use the 28-pin
>>>>> WD1773.
>>>>>
>>>>> Mike Pepe notes in an email on this list on 8/2/06 that the original
>>>>> controller (the one that required 12V on the bus) was the 26-3022.  So
>>>>> that should be the only one you would need to plug into the MPI to use
>>>>> with the CoCo 3.
>>>>>           
>>>>>> Ironically, the only ones that could properly handle hi-density (1.2
>>>>>> or 1.44 MB) drives with some modifications to the controller.
>>>>>>
>>>>>>             
>>>>> This fall Mike Pepe modified his  3029 for high-density and posted
>>>>> a few
>>>>> messages about it on this list.  Last I recall he still needed to
>>>>> finalize the software/firmware modifications.  His notes are here:
>>>>> http://www.doki-doki.net/~lamune/computers/coco/hd-floppy/
>>>>>
>>>>> JCE
>>>>>           
>>>>>> --L. Curtis Boyle
>>>>>>
>>>>>> -- 
>>>>>> Coco mailing list
>>>>>> Coco at maltedmedia.com
>>>>>> http://five.pairlist.net/mailman/listinfo/coco
>>>>>>
>>>>>>             
>
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