Lenovo ThinkPad 770 Technical Reference Manual for the ThinkPad 770 - Page 44
Real-Time Clock Bytes Hex 000-00D, Status Register A Hex 00A, Interrupt 1AH is the BIOS
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Real-Time Clock Bytes (Hex 000-00D): Bit definitions and addresses for the real-time clock bytes are shown in Figure 2-15. Address (Hex) 000 001 002 003 004 005 006 007 008 009 00A 00B 00C 00D Function Seconds Second alarm Minutes Minute alarm Hours Hour alarm Day of week Date of month Month Year Status register A Status register B Status register C Status register D Byte Number 0 1 2 3 4 5 6 7 8 9 10 11 12 13 Figure 2-15. Real-Time Clock Bytes (Hex 000-00D) Note: The setup program initializes status registers A and B when the time and date are set. Interrupt 1AH is the BIOS interface to read and set the time and date; it initializes the registers in the same way that the setup program does. Status Register A (Hex 00A) Bit Function 7 Update in progress (UIP) 6 Countdown chain 1 - resets countdown chain 0 - countdown chain enabled 5 Oscillator enable 0 - oscillator off 1 - oscillator on 4 Bank select 3-0 Rate-selection bits Figure 2-16. Status Register A (Hex 00A) Bit 7 This bit is a status flag that can be monitored. If this bit is 1, the update transfer will soon occur. If this bit 0, the update transfer will not occur for at least 244 µs. 2-22 System Board