Never mind, I managed to reconstruct the raw PROM contents from the cooked dump. Now the AP2000 doesn’t drop characters. Rewritten Parallael Interface Card is on master. A couple of things to beware of:
  • The most obvious difference between “Parallel Printer” and “Centronics” firmware modes (can be selected in DIP Switches menu) is that Centronics mode doesn’t automatically add a line feed after a carriage return.
  • By default, the card doesn’t strip the top bit off characters, and the Apple II sets the top bit of characters. This will print as graphics characters on most printers. You can go into the Machine Configuration and change to 7-bit mode to allow PR#1 etc. to work with normal printers. Of course, if you’re using a program that needs to send 8-bit data to the printer you’ll need to select 8-bit mode again.
  • The PROM driver doesn’t use interrupts for anything. There’s probably no point enabling interrupts.
  • The card seems to have a different idea of how strobe works to everyone else. With negative strobe selected (the default), strobe drops at almost the same time the data becomes valid, as both things happen around the rising edge of the phase 1 clock. Printers tend to treat the falling edge on the strobe as active, so this could glitch.
  • Similarly, the card will reject any active (rising) acknowledge edge while strobe is active, so if the printer responds to the negative edge before the card sends it high again, it miss it and wait forever.
  • To work around this, it’s safest to change the DIP switches to use positive strobe.
  • edit: And don’t change PROM addressing to flat unless you’re testing your own custom PROM – it will blow up spectacularly.

Last edited by Vas Crabb; 10/24/20 05:54 PM.