IBM 560 - Manual (Page 41)

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
6–4 22-stage divider
3–0 Rate-selection bits
Bit 7 When set to 1, this bit indicates that the time-update
cycle is in progress. When set to 0, it indicates that the
current date and time can be read.
Bits 6–4 These bits identify which time-base frequency is being
used. The system initializes these bits to binary 010,
which selects a 32.768-kHz time base. This is the only
value supported by the system for proper timekeeping.
Bits 3–0 These bits allow the selection of a divider output
frequency. The system initializes the rate-selection bits
to a binary 0110, which selects a 1.024-kHz
ThinkPad 560/560E System Board 2-19