There have been several different encoder boards used in Apple ][s. The one shown in the Reference Manual uses 5 chips : U1 7400 U2 7404 U3 555 U4 7400 U5 MM5740 If it is that version, then the control key has one side grounded. The other side is pulled up by R1 (4k7) to +5V. That side of the key also goes to the inputs of U1d (inputs tied together), which inverts the signal. The output of that (which will be high when the control key is pressed, low otherwise) goes to pin 19 on U5, the MM5740 keyboard encoder chip. If you have that version, it would be worth checking that the output of U1d (and pin 19 of U5) do go high when 'control' is pressed and are low otherwise. If not, the components are probably trivial to replace. Also, you might check that the sections of U2 (low 6 bits of the output word) and U1c (again, inputs tied together) are working correctly. Losing the top few bits of the keyboard data will make it appear that control is pressed. Most likrly, though, the MM5740 is dead, and that is non-trivial to replace. I read somewhere that Apple used a custom version in some of their machines, because the keyswitches are in a non-standard matrix pattern (the MM5740 contains a ROM which converts the X,Y coordinates of a key in the matrix into its ASCII code, and it was possible to get versions with custom ROM patterns if you wanted 10000 of them). Many Apple ][s at least in the UK use a different encoder board. I would guess the circuitry is similar in concept, and all you need to do is trace the connections of the control keyswitch (most likely one side is grounded) to the logic, and make sure the signal changes state, at least up to the LSI encoder chip. Again, if that chip has failed, you've got problems. -tony

> something I can't see because it's not out of the box (yet). If the MM5740 > (I'll look it up later, in an old NSC MOS LSI databook) is just a ROM lookup > table, an exacto knife and a few wires will allow it to be adapted to a 2732

It's not. It includes a ROM table, but it's a complete keyboard encoder chip, with the scan counters, etc in it. You could hack a single-chip micro in place of it, but not just a 2732 or simialr. Programming a 8751 or similar (or whatever your favourite microntroller with enough I/O (you might want to use external binary to 1-of-n decoders) is) to replace a keyboard encoder chip is a reasonable first embedded microcontroller project, actually. It's not a time-critical application, so your code doesn't have to be efficient. -tony

> > My thoughts exactly, Tony. There are even enough app-notes dealing with

> problem that one should be able to find one for nearly any single-chipper.

Sure... You want a microcontroller with a fair number of I/O lines (7 data bits + strobe to the host, shift/control/repeat key inputs, key matrix lines) so an 18 pin PIC would not be a good choice (you'd need so many extra TTL chips to get the I/O that you might as well build the whole thing in TTL :-)). But an 8748 or 8751 or 6811-series, or... would be fine. > trick is to find the details on the old MM5740 to enable one to emulate it

If it is that version of the keyboard, the schematic (including the pinout of the MM5740, at least the pins that are used) is in the Apple ][ Reference Manual (it's Figure 17, page 101 in my edition). You also know what codes the keyboard should send to the Apple mainboard, so it's not going to be hard to work out what to do... > single-chipper that can subsequently be patched into the application

Agreed.... Pick the chip you know best -- any of them will be suitable :-) -tony