Ron Kneusel wrote: > Greetings all! > > I have been told that it might be possible to put a 65816 > CPU (from a IIgs I imagine) into a IIe so that one would have > the functional equivalent of the rare 65802. Does anyone know > for certain if this is possible and how to go about doing it? Some people claim to have done this and it appeared to work, but I wouldn't recommend it. The major difference is that the 65816 uses the data bus pins for a second function, namely outputting the bank address during the first half of each cycle. Here is a slightly reworded extract from an article of mine from about 18 months ago that covers the remaining details. Several pins are used for totally different functions on the 65C02 and 65816, and some of these happen to include a reversal of the signal direction. From a quick glance at the pinout, here are the major differences: 65C02/65802 65816 1 Ground Vector Pull (output) 3 Phase 1 clock (output) Abort (input) 5 No Connection Memory Lock (output) 7 Sync (output) Valid Program Address (output) 35 No Connection Emulation status (output) 36 No Connection Bus Enable (input) 38 Set Overflow (input) M/X status (output) 39 Phase 2 clock (output) Valid Data Address (output) (There is also the data bus, which has a bank address on it as mentioned earlier.) The most serious difference is pin 1: if this is tied to ground on the circuit board (as it is on the Apple II motherboard), then plugging in a 65816 will cause its vector pull output to be shorted to ground. This signal is normally high, so this isn't very good for it. Some of the control signals (abort and bus enable) would not be driven by the circuit board, which may cause them to float to an undefined state, increasing power consumption and possibly causing random aborts and bus floats. (This depends on whether the CPU has an internal pullup on these inputs.) The Sync output on the CPU (65C02) goes to all the slots, and can be used by cards to identify an opcode fetch (e.g. for a debugging card). This won't work any more if you replace the CPU with a 65816. The other signals are less of a problem on the Apple II motherboard, as the clock outputs of the CPU are not used, and neither is Set Overflow. On an accelerator, on the other hand, all bets are off. The card might be using the Sync output and clock signals for something important, and putting a 65816 on there would prevent it from operating. Trying to use native mode of the '816 may also cause problems, depending on how the accelerator interacts with the CPU (if it has any timing dependencies or watches instructions for doing some special operations). The bank address being on the data bus during the first half of the cycle is likely to cause continuous signal collisions, which will increase system noise, increase power consumption and reduce reliability. It could also prevent an accelerator from operating. -- David Empson dempson@actrix.gen.nz Snail mail: P O Box 27-103, Wellington, New Zealand