knudsen@ihlpl.ATT.COM (Knudsen) (10/29/88)
Last nite at our monthly meeting of the Chicago OS9 Users' Group, the guest speaker was none other than Chris Burke (half of B&B) himself. I asked him about the BLOB problem and the E-clock gating. He had certainly heard of it! His response was as follows: (1) The Cocos do not gate the peripheral device select SCS- (the FF40 range strobe) with E-clock themselves. [This is probably good, since a device should know ahead of time that it is selected. By "time" I mean the E clock pulse.] (2) So each peripheral should gate its own internal enables with E clock. Some don't, including my old DISTO Ramdisk and early models of the B&B HD adapter. New B&Bs do, and he showed us one with the extra IC on it. (3) He said I could hack the fix into my old B&B as follows: Stick another 74LS00 quad-NAND chip on it somewhere. Feed SCS- into both inputs of one gate (pins 1 & 2) to get de-inverted SCS+ out of pin 3. Feed this to one input of a second gate (pin 4). The other input (pin 5) gets E-clock off the Coco bus. The output on pin 6 is the gated SCSE-. Cut the original SCS- feed from the Coco bus into the PC bus, and feed the new SCSE- into the PC bus. Oh yes, feed Ground to pin 8 and +5 to pin 16, helps a lot ;-). I haven't had any BLOB problems, but then I avoid making new boots like the plague, tho there are several reasons for me to make another one. I may or may not go thru with this mod, depending on how my new boots work out. (4) This isn't BLOB-related, but Chris will soon have a universal Coco-->PC-bus adapter that will handle up to four of ANY PC card. Including an MPU-401 clone board for us MIDI musicians. This will be aimed at hackers who repackage their Coco system into PC cases. [Thanks to the Burkes, we can salvage just about everything of a PC except the motherboard :-) ]. -- Mike Knudsen Bell Labs(AT&T) att!ihlpl!knudsen "Lawyers are like nuclear bombs and PClones. Nobody likes them, but the other guy's got one, so I better get one too."