DS1685/DS1687 3V/5V Real-Time Clocks

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Register C (0Ch)

MSB

LSB

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

IQRF

PF

AF

UF

0

0

0

0

IRQF – The interrupt-request flag (IRQF) 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

Any time the IRQF bit is a 1, the

IRQ pin is driven low. Flag bits PF, AF, and UF are cleared after Register C is read

by the program.

PF – The periodic-interrupt flag (PF) 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–RS0 bits establish the periodic rate. PF is set to a 1 independently of the state of

the PIE bit. When both PF and PIE are 1’s, the

IRQ signal is active and sets the IRQF bit. This bit may be cleared

by reading Register C.

AF – A 1 in the alarm-interrupt flag (AF) bit indicates that the current time has matched the alarm time. If the AIE bit

is also a 1, the

IRQ pin goes low and a 1 appears in the IRQF bit. This bit may be cleared by reading Register C.

UF – The update-ended interrupt flag (UF) bit is set after each update cycle. When the UIE bit is set to 1, the one in

UF causes the IRQF bit to be a 1, which asserts the

IRQ pin. This bit may be cleared by reading Register C.

BIT 3, BIT2, BIT 1, BIT 0 - These are unused bits of the status Register C. These bits always read 0 and cannot be

written.

Register D (0Dh)

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

read. If a 0 is ever present, an exhausted lithium energy source is indicated and both the contents of the RTC data

and RAM data are questionable.

BIT 6, BIT 5, BIT 4, BIT 3, BIT 2, BIT 1, BIT 0 – The remaining bits of Register D are not usable. They cannot be

written and when read will always read 0.