[Coco] new high density controller

[Mike Pepe]

Phill Harvey-Smith wrote:
> Brian Blake wrote:
>> I guess that's going to depend on what you mean by 'interested.' I
>> don't have much in the way of input since most you guys outclass me
>> on the hardwareguruometer by a large margin, but, I am certainly
>> interested in a fdc that can do HD...
> 
> That would be cool.
> 
> Something I once investigated using the Dragon WD2797 controler was 
> running that at 2MHz, giving a data rate of 1Mbits/sec, which it was 
> capapble of as I believe 8" drives used them. There is also a WD2793, 
> which is from a programming interface identical to the WD1793/WD1773, 
> currently used by the CoCo, and can also do the same data rates...though 
> it is prolly harder to get hold of than the Intel chip. Designing a 
> controler around this would have the significant advantage of being able 
> to use existing driver software...even RS-DOS should work un-modified.
> 
> just my 2p :)
> 
> Phill.
> 

Problem with the 2793 is that it's not designed to be switchable between 
the 250k and 500k data rates. It has internal analog circuitry and would 
require some analog ugliness to make it work  as a dual mode controller.

Since the HD rates are really only useful in OS9 anyway- you'd need a 
driver no matter what. So, I think the 1773/82077 hybrid is the way to go.

- It's 100% digital. No pots or passives to worry about, and no 
calibration to be done.
- The 82077's FIFO makes no-halt possible without the dozen or so 
support chips of the DISTO solution.
- It would support low density, high density (even 1.2MB drives), and ED 
disks as well as QIC/Travan tapes.
- You could actually have 4 double sided devices if you wanted to.
- And, 100% compatible with disk basic.