BigEd wrote:
Jac - were you running the Propeller with a 3V supply, but with all I/O at 5V? That would be a sort of hybrid solution, moderately convenient, all it needs is a 3V regulator. Or a big resistor!
I ran the Propeller with a 3.3V supply (the QuickStart board has a built-in 3.3V regulator so I was forced to do it that way) and it was attached to the 5V address bus and data bus, and the R/!W and Phi2 outputs of the NMOS 6502. Data in both directions was transfered without problems (at 1MHz) and the Propeller didn't even get warm.
The MicroKIM has pull-up resistors on the data bus if I'm not mistaken, which helps with the 3.3V signals that the Propeller would put on the data bus, but I've used the Propeller on a 6502 (NMOS) system without pullups too.
Reversely, the Propeller seems to be fine with the 5V input signals. It's CMOS based so the inputs have a very high impedance. The thing that kills the I/O pins is current, and if the voltage is too high, the diode will sink too much current to keep the internal voltage down, and destroys itself. Based on the specifications of the Propeller, you should have a 2700 Ohm series resistor on input pins to make them 5V tolerant. There's an article on the Internet somewhere that explains it better than this.
Either way, direct connections without series resistors worked fine in my case but "your mileage may vary". I won't take responsibility if you let the Magic Smoke escape. By the way, if the 6502 in your system happens to be a CMOS (65C02) version, it also has high impedance inputs so if there are 2k7 series resistors on the data bus, the Propeller should still be able to drive the data bus of the 65C02 high. I must have also tried 2k7 series resistors in an NMOS 6502 system at 5V but I think I must have; when I started on my Propeddle project, I didn't have many chips and I was very careful not to fry anything.
Anyway, I always had the power supply of the Propeller at 3.3V, not 5V.
===Jac