[Coco] 1.2 MEG DRIVES might be ot

[Phill Harvey-Smith]

Gene Heskett wrote:
> On Sunday 16 July 2006 17:39, Phill Harvey-Smith wrote:
>> George's Coco Address wrote:
[snip!]

>> As with 1.44MB drives they may be usable on the CoCo/Dragon in double
>> density mode, as 80 track drive giving 720K/disk.
> 
> That will be if the jumper that slows them down to 300 rpm can be found, 
> by default they spin at 360 rpm.  Once thats done however, they make 
> great DSDD 720K drives (I have one such here) that can also *read 40 
> track disks.  However, it takes the same jumper speed slowdown to make 
> them work with the 40 track disks also.

I seem to remember that there is a line on the interface cable that 
could also control this, I think this is how the the PC switched 
densities, If my memory serves me correctly, this was pin 1, might be 
worth googling that, if I get a chance I'll try it sometime :)

> That about speed being said, there were some aftermarket controllers 
> that used the fujitsu 8877 fdc chip, and a determined experimentor 
> could convert one of those to handle the 500kilobaud data rate just as 
> easily as with the original 12 volt only controller.  Just follow the 
> basic outline of the instructions for the 12 volt model.

Yeah, I did manage by changing the clock crystal, to run a DragonDos 
controler (which is WD2797 based), at 500k, and successfully read 
sectors off a PC formatted 1.44M disk, though I had to run the Dragon 
over clocked in address dependent mode, which is fine for a 32K ROM 
based machine but no good at all for Nitros :( Would proly be ok on a 
CoCo 3 tho :)

> *don't ever write to a 40 track disk in one of these, the disks data 
> will be forever trashed when then loaded into a 40 track drive.

People keep saying this, but I've been using switchable 40/80 track 
drives for about 20 years now and never encountered this problem :)

Phill.

-- 
Phill Harvey-Smith, Programmer, Hardware hacker, and general eccentric !

"You can twist perceptions, but reality won't budge" -- Rush.