68k:Ports:600000

This port controls I/O from pins 99 and 100 on the ASIC. It's used to check battery voltage on all calcs, and to control LCD contrast on the TI-92.

• Bit 7: Pin 100 output enable (keep =0)
• Bit 6: Pin 99 output enable (keep =0)
• Bit 5: Data to pin 100 (TI-92: used for LSB of LCD contrast)
• Bit 4: Data to pin 99 (not used)
• Bit 3: Data from pin 100 (not used)
• Bit 2: Data from pin 99 (1 if batt. voltage is above trigger level (see 600018)