Wednesday, September 23, 2015

Making speed control easier

Just a quick post today about a couple of enhancements to make it easier to select CPU speed on the MEGA65:

1. The CPU now defaults to be locked to 48MHz, so that it is as fast as possible by default.

2. To enable slower speeds (under C128/C65 speed control register direction): POKE0,64

3. To force the CPU back to full speed: POKE0,65

4. The ASC/DIN key on a real C65 keyboard will have a similar effect to the above.

The POKE 0 system uses a special over load of the CPU DDR port at $00 - if $40 or $41 are written, then the DDR is not changed, but instead the CPU speed control function is followed instead.