thad@cup.portal.com (Thad P Floryan) (01/06/91)
Recently, someone (Little David? :-) commented about building the ICUS two-HD P5.1 modification directly on the 3B1's motherboard and wanting to use the existing 26LS31 to drive the 2nd HD, but discovered the "uncomitted" pins were, in fact, being used for "something." Then Gil asked (paraphrased) "Any idea where they're being used?" After I posted my "new boot ROM code idea" earlier today, I looked again at the schematics, page 14, and said "WTF?!" The first set of schematics I examined were using pairs of Schottky inverters from a 74LS14 to send the "serial" signals (TxD and *RST) to the keyboard; the set of schematics I glanced at THIS time showed the other pins of the 26LS31 being used for that purpose. So I checked the 3rd set of schematics, and find: motherboard serial drivers to keyboard ------------- -------------------------- D-08-00222-00 74LS14 D-08-00225-00 26LS31 D-08-00230-00 74LS14 So that explains why there ARE some other pins being used on the 26LS31 on SOME 3B1 systems. Thad P.S. And one person brought a "D-08-00216-00" motherboard to the last Users' Group meeting and, whew, was THAT board different. Even the pinouts of the 34-pin connector to the floppy drive were COMPLETELY REVERSED from all other 3B1 systems I've seen; at least the pinnings were silkscreened on the board. Makes me wonder just how MANY "something new and completely different" 3B1 systems there ARE out there? C0WABUNGA!!! Thad Floryan [ thad@cup.portal.com (OR) ..!sun!portal!cup.portal.com!thad ]