tjpadula@phoenix.Princeton.EDU (Thomas John Padula) (03/27/89)
Gotta problem with my trusty old Apple II+. It's a 1978 vintage machine, and has (so far) served me well over the years. I occasionally design my own cards and use them in the machine, but I have now run into a problem I've never seen before- any and all ideas would be appreciated. To whit: I have some signal processing circuitry I'm working on on an external board. It has its own power supply, and is connected to the apple via a 5' ribbon cable plugged into a slot which carries the relevant apple busses and signals. Among other things, I have a Videx Videoterm 80-column card with softswitch and a Passport MIDI interface. Here's the problem- these three devices don't like each other. Any two of them in the machine (along with Disk II card and apple language card and anything else) will work fine, no glitches or bugs, predictable card behavior. When all three are plugged into the computer (80-column in slot 3, the other two can go in any slot) the computer frequently will not start (no screen, no beep, nothing) or if it does it rarely makes it through the bootup process. If it makes it throught that, it acts as if it is being showered with interrupts- very slow, segmented operation (example: the error beep isn't a continuous tone- it's bits of beeps put together over a longer period of time than usual). The development hardware does not use phantom slots (only looks at the D-bus when DS' is active) and is generally well behaved. The MIDI card was damaged awhile ago by the friend I got it from, but has been patched into working. It has a very simple internal structure (it's basically a UART with some logic support chips) and doesn't bomb out any other cards. The Videx card is godawfully complicated in its addressing, and I have no idea how it interfaces with the computer (I just use it for 80 columns occasionally). BTW, I know the apple isn't starving for power- the development board draws only 30 ma, and the apple can power it and seven other cards at the same time (I've picked up a lot of toys over the years), as long as the MIDI card or 80-column card are left out. I don't normally run the machine with a load of cards in it. I am an electrical engineer with a lot of hardware experience with the apple, but this one eludes me. Anyone with any ideas or more questions please email me, as I don't get to read news very often. Thanks for any and all responses. I really need all three cards to develop this system. Keep hacking. "alternate mnemonic- EDV #v - Eject disk with velocity V (for 3.5 drives)" tjpadula@phoenix.Princeton.EDU Thomas J. Padula tjpadula@winnie.Princeton.EDU 212 Foulke Hall princeton!phoenix!tjpadula Princeton University, NJ 08544 tjpadula@phoenix.BITNET 609-734-7411