[Coco] Disk drive question

[Mark Marlette]

Robert Brose of our Twin Cities Color Computer Club created this mod. 

This mod allows the 500k baud xfer and supports HD disk - 360K disks. Control through the descriptor. 

I did this mod once...This is an extreme mod to the controller. Almost easier to layout a new board! 

Not sure where / if the MB8877A is still obtainable or not. 

Works great. 

Mark 
Cloud-9 


----- Original Message ----- 
From: "gene heskett" <gheskett at wdtv.com> 
To: coco at maltedmedia.com 
Sent: Sunday, January 22, 2012 10:34:31 AM 
Subject: Re: [Coco] Disk drive question 

On Sunday, January 22, 2012 11:28:52 AM hhos at st-tel.net did opine: 

> > Sorry, it was the somewhat rare 26-3022 drive controller that required 
> > 12v. 
> > The 26-3029, FD-500/501/502 controllers were 5v. There is a rather 
> > involved 
> > hardware hack to make the 26-3022 capable of addressing the 1.44 Meg 
> > floppies too. For most practical use any drive works with any 
> > controller. 
> > 
> > Bruce W. 
> 
> This is a link to instructions for that hardware hack. 
> 
> http://www.reocities.com/idezilla/CoCoZilla/hdtext.html 
> 
> I have not tried it, but without going through all of this, I understand 
> that just dropping in a 8877(A) chip, to replace the WDC1793 in the 
> original Tandy controller, will eliminate the need for +12VDC. Can 
> anyone confirm this? 
> 
> HH 
> 
It may be slightly more complex than that, as in switching a 12 volt pin to 
have it wired for 5 volts. Having looked at its specs (I even had a sheet 
around here someplace) I also got the impression it would also work at 500 
kilobaud allowing the use of many of the more modern drives. I have 
encountered 3.5" drives that will not function at all with the coco's 250 
kilobaud controllers. A full megabaud or even 2 is likely beyond its reach 
though. 

?? Does anyone know where the 8877 can be obtained today? 

Cheers, Gene 
-- 
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soap, ballot, jury, and ammo. Please use in that order." 
-Ed Howdershelt (Author) 
My web page: <http://coyoteden.dyndns-free.com:85/gene> 
Do you remember when you only had to pay for windows when *you* broke them? 

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