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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.
Figure
2-15. Real-Time Clock Bytes (Hex 000–00D)
Address
(Hex)
Function
Byte Number
000
Seconds
0
001
Second alarm
1
002
Minutes
2
003
Minute alarm
3
004
Hours
4
005
Hour alarm
5
006
Day of week
6
007
Date of month
7
008
Month
8
009
Year
9
00A
Status register A
10
00B
Status register B
11
00C
Status register C
12
00D
Status register D
13
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)
Figure
2-16. 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
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
µ
s.
2-22 System Board
Summary of Contents for ThinkPad 770
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Page 6: ...vi...
Page 10: ...x Preface...
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