knudsen@ihwpt.UUCP (mike knudsen) (11/03/86)
Because lots of Coco-I & II software and hardware aren't compatible with the Coco III, some folks have wished out loud that Radio Shack had warned us in advance, especially about the FExx page. Last nite I had to dig into my Motorola manual for something else, and I noticed that under the SAM chapter it described FE00-FEFF as "reserved for MPU enhancements" (MPU is the 6809, not the SAM, weird) and that the portion of the FFxx I/O page available for add-ons is much more restrictive than even Tandy's official range, which I believe is FF60-FF7F. You could interpret Motorola as saying that only FF40-FF5F is free -- most of that is taken up by Tandy's disk controller that ghost-addresses all over the place. I didn't check my old Coco-I tech manual to see how much of this had been reproduced there -- if it has, then Tandy had indeed given a clear warning. Of course like everyone else I figured "enhancements -- sure, when I can ice skate in Hell" and wrote code that lay all over FExx. Lucky I didn't sell it. PS: There is plenty of I/O space in FF04-FF1F and FF24-FF3F, left over from the two PIA chips. To use it, a peripheral must decode all the bits itself and pull down the Phantom line (I forget it's official name) to keep the ghosty PIAs from fighting it. That Phantom lead was a great addition to the Coco cart slot (it disables all I/O stuff inside from responding for a cycle) -- too bad no commercial outfits used it. Don't know how much it works on the III, tho. -- Mike J Knudsen ...ihnp4!ihwpt!knudsen Bell Labs (AT&T) (312)-979-4132 (work) Nobody pays for my opinions, which are mine alone. "A mind is a terrible thing to waste, but the pay is good."