IBM Personal System/2 60 - Status Registera

Real-Time Clock Bytes (Hex 000-00D)
Bit definitions and addresses for the real-time clock bytes are shown
in the following figure.
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
oos Year 9
00A Status Register A 10
00B Status Register B 11
00CG Status Register C 12
00D Status Register D 13
Figure 3-9. Real-Time Clock Bytes
Note: The Setup program initializes status registers A, B, C, and D
when the time and date are set. Interrupt hex 1A is the BIOS
interface to read and set the time and date and it initializes the
register the same way as the Setup program.
Status Register A (Hex 00A)
Bit Function
7 Update in Progress
6-4 22-Stage Divider
3-0 Rate Selection Bits
Figure 3-10. Status Register A
Bit7 When set to 1, this bit indicates the time-update cycle is in
progress. When set to 0, it indicates the current date and
time can be read.
Bits6-4 These three divider-selection 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
time-keeping.
Model 60 System Board — October 1990 3-13