ASM Program Size Limitation
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Michael Vincent - michael@radicalsoft.org


** WHY PROGRAMS ARE LIMITED TO ~8 KB

TI was afraid that people would pirate applications by converting the code into a program. So they restricted ASM programs' size to about 8 K, thus preventing 16 K converted apps from running as normal ASM programs.

** WHAT TI DID

TI implemented a hardware restriction that locks up the calc if the program counter (PC) is above C000h. Since ASM programs start at 9D95h, they can't run code past about 8.8 K into the program.

** WHAT THIS MEANS FOR YOU

Programs can still access sprites, strings, data, etc. above C000h, they just can't run anything above that. This restriction does not affect most programs. If you have a large program, you can copy subroutines to saferam and call them from there, hence bypassing the limitation.

** A WORKAROUND?

On the TI-83 Plus Silver Edition, it is possible to swap a different RAM page into the C000h-FFFFh area. The hardware will allow code to be executed from pages 82h-87h. This is not recommended at all unless you understand what you are doing.

** MYTHS

Unlike what some people believe, disabling interrupts and not using any ROM calls will not allow code to run above C000h. It is a hardware limitation and cannot be bypassed normally.