APD Info
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Michael Vincent - michael@radicalsoft.org



** WHAT IS IT

APD (Automatic Power Down) is designed by TI to prevent you from draining your batteries inadvertantly leaving your calc on. After about 4 minutes of inactivity, the calculator will power down.

** HOW IT WORKS

There are 2 memory locations associated with APD, apdSubTimer (8448h) and apdTimer (8449h). While the TI-OS is running, it decrements (apdSubTimer) until it's zero, then resets it to $FF and decrements (apdTimer). When (apdTimer) is zero, the TI-OS stores the current screen image (from the LCD controller) in APD RAM (86ECh, 768 bytes) and then turns off the calculator. Upon power on, the APD counter is reset, the screen is restored, and the TI-OS resumes as normal.

** APD COUNTER

The reset value for the APD COUNTER is 74h. So:

ld a,$74
ld (8449h),a

Will reset the APD counter. Generally you don't need to worry about resetting the apdSubTimer, as the minor variance in the value is only a second or two of APD time.