LPC Interface Bridge Registers (D31:F0)
8-48
82801AA and 82801AB Datasheet
8.6.2.3
RTC_REGC—Register C (Flag Register)
RTC Index:
Default Value:
Lockable:
0Ch
00U00000 (U: Undefined)
No
Attribute:
Size:
Power Well:
RO
8 bits
RTC
Writes to Register C have no effect.
8.6.2.4
RTC_REGD—Register D (Flag Register)
RTC Index:
Default Value:
Lockable:
0Dh
10UUUUUU (U: Undefined)
No
Attribute:
Size:
Power Well:
R/W
8 bits
RTC
Bit
Description
7
Interrupt Request Flag (IRQF).
Interrupt Request Flag = PF * PIE + AF * AIE + UF *UFE. This also
causes the CH_IRQ_B signal to be asserted. This bit is cleared upon RSMRST# or a read of Register
C.
6
Periodic Interrupt Flag (PF).
This bit is cleared upon RSMRST# or a read of Register C.
1 = Periodic interrupt Flag will be one when the tap as specified by the RS bits of register A is one.
0 = If no taps are specified, this flag bit will remain at zero.
5
Alarm Flag (AF).
Alarm Flag will be high after all Alarm values match the current time. This bit is
cleared upon RTCRST# or a read of Register C.
4
Update-ended Flag (UF).
Updated-ended flag will be high immediately following an update cycle for
each second. The bit is cleared upon RSMRST# or a read of Register C.
3:0
Reserved. Will always report 0.
Bit
Description
7
Valid RAM and Time Bit (VRT).
1 = The Valid Ram and Time bit is set to one when the PWRGD (power good) signal provided is high.
This feature is not typically used.
0 = This bit should always be written as a 0 for write cycle, however it will return a 1 for read cycles.
6
Reserved. This bit always returns a 0 and should be set to 0 for write cycles.
5:0
Date Alarm.
These bits store the date of month alarm value. If set to 000000, then a don’t care state
is assumed. The host must configure the date alarm for these bits to do anything, yet they can be
written at any time. If the date alarm is not enabled, these bits will return zeros to mimic the
functionality of the Motorola 146818B. These bits are not affected by RESET.