DS17885/DS17887

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REGISTER C

MSB

LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

IRQF

PF

AF

UF

0

0

0

0

IRQF – Interrupt Request Flag. This bit is set to a 1 when one or more of the following are true:

PF = PIE = 1

WF = WIE= 1

AF = AIE = 1

KF = KSE= 1

UF = UIE = 1

RF = RIE = 1

i.e., IRQF = (PF x PIE) + (AF x AIE) + (UF x UIE) + (WF x WIE) + (KF x KSE) + (RF x RIE)

Register C is read by the program.

PF – Periodic Interrupt Flag. This is a read-only bit that is set to a 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 a 1

IRQF bit. The PF bit is cleared by a software read of Register C.

AF – Alarm Interrupt Flag. A 1 in the AF bit indicates that the current time has matched the alarm

C clears AF.

UF – Update Ended Interrupt Flag. This bit is set after each update cycle. When the UIE bit is set to 1,

BIT 3 to BIT 0 – These are unused bits of the status Register C. These bits always read 0 and cannot be

written.

REGISTER D

MSB

LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

VRT

0

0000

00

VRT – Valid RAM and Time. This bit is a read-only status bit. When VRT = 0, the RTC and RAM data

are questionable and indicates that the lithium energy source has been exhausted and should be replaced.

BIT 6 to BIT 0 – The remaining bits of Register D are not usable. They cannot be written and, when

read, they always read 0.