Found a couple of diagnostic disks for the silentype:

"Apple II+ Products diagnostic 652-0334.dsk"
"Apple II Peripherals diskette 077-0217-A.dsk"

[Linked Image from]
[Linked Image from]

I dusted off my old silentype driver and it wasn't working, and I traced it to not initializing an array of doubles. I had code that would compare it to 0.0 and 1.0 and clamp it to that range, so I thought it wouldn't be a problem to leave it unitialized, but if it gets memory that is interpreted as NaN that comparison silently fails.

I did learn that you can initialize an array of doubles like this: double myarray[8] = {0.0}; Expecting uninitialized variables to be 0 is a hard habit to break. 8-)