Real-Time Clock
5/DS12C87A
Control Register C
MSB
LSB
BIT 7
IRQF
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
PF
AF
UF
0
0
0
0
Bit 7: Interrupt Request Flag (IRQF). This bit is set to
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.
1 when any of the following are true:
PF = PIE = 1
AF = AIE = 1
UF = UIE = 1
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.
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.
Bits 3 to 0: Unused. These bits are unused in Register
C. These bits always read 0 and cannot be written.
Control Register D
MSB
LSB
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
VRT
0
0
0
0
0
0
0
Bit 7: Valid RAM and Time (VRT). This bit indicates
the condition of the battery connected to the V pin.
the RTC data and RAM data are questionable. This bit
is unaffected by RESET.
BAT
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
Bits 6 to 0: Unused. The remaining bits of Register D
are not usable. They cannot be written and they always
read 0.
____________________________________________________________________ 17
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
