DS12885_10 Datasheet, PDF (17/22 Pages) Maxim Integrated Products – Real-Time Clocks

Real-Time Clocks
MSB
BIT 7
IRQF
BIT 6
PF
BIT 5
AF
BIT 4
UF
Bit 7: Interrupt Request Flag (IRQF). This bit is set to
1 when any of the following are true:
PF = PIE = 1
AF = AIE = 1
UF = UIE = 1
Any time the IRQF bit is 1, the IRQ pin is driven low.
This bit can be cleared by reading Register C or with a
RESET.
Bit 6: Periodic Interrupt Flag (PF). This bit is read-
only and is set to 1 when an edge is detected on the
selected tap of the divider chain. The RS3 through RS0
bits establish the periodic rate. PF is set to 1 indepen-
dent of the state of the PIE bit. When both PF and PIE
are 1s, the IRQ signal is active and sets the IRQF bit.
This bit can be cleared by reading Register C or with a
RESET.
Control Register C
LSB
BIT 3
0
BIT 2
0
BIT 1
0
BIT 0
0
Bit 5: Alarm Interrupt Flag (AF). A 1 in the AF bit indi-
cates that the current time has matched the alarm time.
If the AIE bit is also 1, the IRQ pin goes low and a 1
appears in the IRQF bit. This bit can be cleared by
reading Register C or with a RESET.
Bit 5: Update-Ended Interrupt Flag (UF). This bit is
set after each update cycle. When the UIE bit is set to
1, the 1 in UF causes the IRQF bit to be a 1, which
asserts the IRQ pin. This bit can be cleared by reading
Register C or with a RESET.
Bits 3 to 0: Unused. These bits are unused in Register
C. These bits always read 0 and cannot be written.
MSB
BIT 7
VRT
BIT 6
0
BIT 5
0
BIT 4
0
Bit 7: Valid RAM and Time (VRT). This bit indicates
the condition of the battery connected to the V_BAT pin.
This bit is not writeable and should always be 1 when
read. If a 0 is ever present, an exhausted internal lithi-
um energy source is indicated and both the contents of
BIT 3
0
BIT 2
0
Control Register D
LSB
BIT 1
0
BIT 0
0
the RTC data and RAM data are questionable. This bit
is unaffected by RESET.
Bits 6 to 0: Unused. The remaining bits of Register D
are not usable. They cannot be written and they always
read 0.
____________________________________________________________________ 17