mam@gvgspd.GVG.TEK.COM (Mark A. Matthews) (10/31/88)
What's between my MIDI interface and my mac is a cable :) What's *in* my MIDI interface is much more interesting. Cracking open my Passport MIDI interface for the Macintosh reveals the following goodies: 2 5-pin DIN connectors (laleled "in" and "out") 1 cable with 9-pin D-connector, suitable for attaching to a Mac 3 1N914-type diodes in various spots about the board. 1 1N752A (zener? All my good databooks are at work, where I'm not) 3 10 uF 16V capacitors 5 resistors, various values and locations 1 8-pin sip resistor package 4.7K 3 bypass capacitors 1 2N4401 transistor 1 6N138 Opto-isolator (near the "in" connector) 1 4Mhz crystal, with 5 pf capacitor in parallel 1 74HC04 1 74HC74A Pretty simple. They certainly make a healthy profit on these puppies. But then again, now that I work for a living (as opposed to a starving student) I don't mind so much. I haven't tried to create a schematic from it, but it is apparent that the power is stolen from the Mac. The 74HC04 is being used as an oscillator for the 4 Mhz crystal. The output from the osc. is fed to the clock input of one of the 74HC74A flip-flops which appears to be wired in a dive-by-4 fashion. I *think* the output of this is capacitively coupled to the external clock pin of the D9 connector. Rats. Now you've got me curious and I'll just have to draw up a schematic to see just what this little box is supposed to do. Oh. One more note: On the foil side of the board (it is single-sided), it has the phrase "McMIDI", "(C) 1986 ADON CORP", "PDI", "UMC-UL", and "06-88". -Mark (mam@gvgspd.GVG.TEK.COM -or- ...!tektronix!gvgpsa!gvgspd!mam)