[Coco] Any documentation or info on Tandy's Coco hard disk controller?

[John Guin]

 Hello all,

I managed to snag one of these hard disk controllers at a garage sale, and
it powers up to "Disk Extended Basic 1.1" on my Coco2.

But that's all I can do with it - I have no documentation for it otherwise.
Does anyone know anything about it or where to point me for docs?  I looked
through Marty Goodman's hard disk article from the Rainbow (July 89?), but
it did not mention the Tandy controller.

As always, thanks,
John Guin