prindle@NADC.ARPA (Frank Prindle) (08/21/89)
Some experimentation has revealed that a more appropriate value for the cap- acitor in the posted MIDI interface clock circuit is NOT 51pf., but more like 500pf. (470pf. or 510pf. will do quite nicely). With a 6502 clock crystal I purcahsed at Active Electronics, the clock circuit would not reliably lock in at 2MHz. with the 51pf. capacitor, but just ran free at a higher frequency; replacing this with 500pf. cured the problem. Even higher values do not seriously affect the frequency, but somewhat slow the positive going edge of the clock. I hope this error has not caused anyone a major headache. Also, on the posted schematic, the output pin of the 74LS30 was not labeled. If you haven't already looked this up, it is pin 8. I am in the process of building a triple personality board which fits inside an old Commodore cartridge case. The two DIN sockets and a 16-pin DIP socket are on part of the board that sticks out the back of the case. One of three jumpered headers plugs into the DIP socket and selects the personality (JMS, Sequential, or Passport). If any major problems crop up, I'll post a follow-up. Sincerely, Frank Prindle Prindle@NADC.arpa