Michael J. Mahon wrote:
David Schmenk wrote:aiiadict@gmail.com wrote:On Apr 30, 8:32 am, David Schmenk <dschm...@YUCH.gmail.com> wrote:the only bi-directional parallel card I know of is the Apple Parallel Interface Card...I think a few people figured this out, have you noticed what they go for on ePay? Its easier and more flexible to just plug a 6522 (pretty cheapfrom JDR) into a LittleProto board. BTW, the LittleProto board rocks.I have schematics for a 6522 Apple II interface card. 6522 has some neat features besides I/O ports RichIts pretty much a direct connection. I just had to run phi1 through an inverter as the only other chip. Why didn't Woz include phi2 on the bus? One of the great mysteries. I agree with you and Michael that the timers and interrupts are great features - the reason I put mine together.I think that Phi1 and Phi2 are supposed to be non-overlapping clocks, so an inverter may leave a little overlap. The usual approach is to delay Phi0 (which *is* on the bus) by several nanoseconds by using an RC delay feeding an inverter or Schmitt trigger. (Some people skip the gate and directly clock the 6522 from the RC, but that's not SOP. ;-) There's a Mockingboard schematic on the web that shows this approach. Articles were written about this in the 1980s... ;-) -michael NadaPong: Network game demo for Apple II computers! Home page: http://members.aol.com/MJMahon/ "The wastebasket is our most important design tool--and it's seriously underused."
The 6522 was designed to hook straight up to phi2. Oddly, Woz did put phi2 on the Apple1 bus. Using a 7404 to invert Phi1 is probably living on the edge, but works for my purposes - I'm a rebel :-)
Dave...