Dallas Maxim DS12885, Manual

DS12885/DS12887/DS12887A/DS12C887/DS12C887A

Real-Time Clock

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17

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

.

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.

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

IRQF

PF

AF

UF

0

0

0

0

Control Register C

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

VRT

0

0

0

0

0

0

0

Control Register D

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

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.

MSB                                                                                                                                                                           LSB

MSB                                                                                                                                                                           LSB