mdj wrote:
Michael J. Mahon wrote:IIRC, the 5.25" drives must be at the end of the daisy-chain, so the last smartport device must synthesize drive 1 and 2 select lines for the downstream devices, and must also pass on (or regenerate) all the standard 5.25" vrive signals.That sounds reasonable, yes.I expect that there is an signal line that a drive supplies to the interface that says whether it is a smartport device or not, and the interface responds accordingly, even through intermediate smartport devices.Hmm, I'm not sure how, since the //c Smartport, Liron card and 5.25" controller card are essentially identical, and contain signalling that's only relevant to 5.25" drives.
There are several "redundant" power wires on the Disk ][ interface, and if the Smartport interface treats one of these as an input and a smartport device ties it low, then the interface will have a simple level to indicate smartport vs. Disk ][. This is all speculation--if I get desperate I'll have to go look at a schematic. ;-) Of course, once the controller knows it's talking to a smartport device, there's lots of protocol to exchange information.
I seem to recall there was a modification made to analog controller board in the Platinum 5.25" drives that allowed them to respond to a ID request while still essentially being 'dumb' devices - the Apple 3.5" and Superdrive have the same feature, I think.
I doubt that--except for selectively wiring the redundant power lines as noted above.
Surely the electrical characteristics of SmartPort are documented somewhere? Perhaps in one of the IIGS reference manuals I don't have.
I'm thinking I'd start in the IIc Technical Reference Manual... -michael New, faster SUDOKU v2.0 solver for Apple II's! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."