Port Number: 20h
Function: CPU Speed Port
Not present on the TI-83+ Basic!
This port controls the calculator's CPU speed. The CPU can be set to run at either 6MHz or 15MHz with this port.
- 00h : The CPU is running at 6MHz.
- 01h: THe CPU is running at 15MHz.
- 00h : Set the CPU to 6MHz.
- 01h: Set the CPU to 15MHz.
This port is not available on the normal TI-83+. On the normal TI-83+ this port is a shadow of Port 00h.
in a, (2) and 80h jp z, NoCPUGoverner rlca ;Move the 1 bit in bit 7 to bit 0 (80h -> 01h) out (20h), a NoCPUGoverner:
Michael Vincent documented another method to set the CPU speed (which is probably faster than my example).
in a, (2) rla sbc a, a out (20h), a
The only side effect of this is that on the TI-83+ Basic this will cause both linkport lines to go high - which shouldn't matter too much if you're not using the linkport at that time, especailly since both lines are high normally...
Credits and Contributions
- Michael Vincent: Documentation and his faster approach as found here.