output frequency and a 976.562-microsecond periodic
interrupt rate.
Status Register B (X
'
00B
'
)
Figure
2-17. Status Register B (X
'
00B
'
)
Bit
Function
7
Set
6
Enable periodic interrupt
5
Enable alarm interrupt
4
Enable update-ended interrupt
3
Enable square wave
2
Date mode
1
24-hour mode
0
Enable daylight-saving time
Bit 7
If set to 0, this bit updates the cycle, normally by
advancing the count at a rate of one cycle per second. If
set to 1, it immediately ends any update cycle in
progress, and the program can initialize the 14 time bytes
without any further updates occurring until this bit is set
to 0.
Bit 6
This is a read/write bit that allows an interrupt to occur at
a rate specified by the rate and divider bits in status
register A. If set to 1, this bit enables the interrupt. The
system initializes this bit to 0.
Bit 5
If set to 1, this bit enables the alarm interrupt. The
system initializes this bit to 0.
Bit 4
If set to 1, this bit enables the update-ended interrupt.
The system initializes this bit to 0.
Bit 3
If set to 1, this bit enables the square-wave frequency as
set by the rate-selection bits in status register A. The
system initializes this bit to 0.
Bit 2
This bit indicates whether the binary-coded-decimal (BCD)
or binary format is used for time-and-date calendar
updates. If set to 1, this bit indicates the binary format.
The system initializes this bit to 0.
Bit 1
This bit indicates whether the hours byte is in 12-hour or
24-hour mode. If set to 1, this bit indicates the 24-hour
mode. The system initializes this bit to 1.
ThinkPad 560Z System Board
2-21
