[Coco] new high density controller

[Mike Pepe]

Phill Harvey-Smith wrote:

> Humm acording to the data sheet that's what the /ENMF & 5/8 pins are
> for, they allow you to run the chip at 2MHz, and internally divide the
> clock by 2.
> 
> The passives required are only really a couple of pots, a couple of
> resistors and a diode.
> 

The values for the components that drive the pump pin are different for 
the two data rates.

> Though the calibration of the WD chip isn't that hard, it does require a 
> scope :)

Exactly

> Though I guess you would need more glue logic, unless you use a CPLD or 
> something like that.

Maybe less. It depends on how I do it.

> Yeah that was a weekness of Tandy's interface, though to be fair that is 
> down to the extra logic, all the FDC chips used in the CoCo & Dragon are 
> capaple already of supporting 4 DS drives, it's just that in the RS-DOS 
> case the external logic only supports 3 :(

Well, that can be corrected now at least.

> I'll have to go take a look at the Intel's data sheet, got a pointer ?

I'll have to make it available I guess, I'm not sure how I found it in 
the first place!