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82801AA and 82801AB Datasheet
8-47
LPC Interface Bridge Registers (D31:F0)
8.6.2.2
RTC_REGB—Register B (General Configuration)
RTC Index:
Default Value:
Lockable:
0Bh
U0U00UUU (U: Undefined)
No
Attribute:
Size:
Power Well:
R/W
8 bits
RTC
Bit
Description
7
Update Cycle Inhibit (SET).
Enables/Inhibits the update cycles. This bit is not affected by RSMRST#
nor any other reset signal.
0 = Update cycle occurs normally once each second.
1 = A current update cycle will abort and subsequent update cycles will not occur until SET is
returned to zero. When set is one, the BIOS may initialize time and calendar bytes safely.
6
Periodic Interrupt Enable (PIE).
1 = The Periodic Interrupt Enable (PIE) bit allows an interrupt to occur with a time base set with the
RS bits of register A. This bit is cleared by RSMRST#, but not on any other reset
5
Alarm Interrupt Enable (AIE).
1 =The Alarm Interrupt Enable (AIE) bit allows an interrupt to occur when the AF is one as set from an
alarm match from the update cycle. An alarm can occur once a second, one an hour, once a day,
or one a month. This bit is cleared by RTCRST#, but not on any other reset
4
Update-ended Interrupt Enable (UIE).
1 = The Update-ended Interrupt Enable (UIE) bit allows an interrupt to occur when the update cycle
ends. This bit is cleared by RSMRST#, but not on any other reset
3
Square Wave Enable (SQWE).
The Square Wave Enable bit serves no function in this device, yet is
left in this register bank to provide compatibility with the Motorola* 146818B. There is not SQW pin on
this device. This bit is cleared by RSMRST#, but not on any other reset.
2
Data Mode (DM).
The Data Mode (DM) bit specifies either binary or BCD data representation. This
bit is not affected by RSMRST# nor any other reset signal.
1= Binary
0 = BCD.
1
Hour Format (HOURFORM).
This bit indicates the hour byte format. This bit is not affected by
RSMRST# nor any other reset signal.
1 = twenty-four hour mode.
0 = twelve-hour mode. In twelve hour mode, the seventh bit represents AM as zero and PM as one.
0
Daylight Savings Enable (DSE).
The Daylight Savings Enable bit triggers two special hour updates
per year when set to one.
1 = a) Update on the first Sunday in April, where time increments from 1:59:59 AM to 3:00:00 AM.
b) Update on the last Sunday in October when the time first reaches 1:59:59 AM, it is changed to
1:00:00 AM. The time must increment normally for at least two update cycles (seconds) previous
to these conditions for the time change to occur properly.
0 = These special update conditions do not occur when the DSE bit is set to zero. The days for the
hour adjustment are those specified in United States federal law as of 1987, which is different than
previous years. This bit is not affected by RSMRST# nor any other reset signal.