DS17885 Dallas, DS17885 Datasheet - Page 11

• Manufacturer Part Number: DS17885
• Description: (DS17886 / DS17887) 3V/5V Real-Time Clock
• Manufacturer: Dallas

REGISTER C
IRQF – Interrupt Request Flag. This bit is set to a 1 when one or more of the following are true:
Any time the IRQF bit is a 1, the
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
independent of the state of the PIE bit. When both PF and PIE are 1s, the
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
time. If the AIE bit is also a 1, the
C clears AF.
UF – Update Ended Interrupt Flag. 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
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
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.
This bit indicates that status of the V
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.
MSB
MSB
BIT 7
BIT 7
IRQF
VRT
i.e., IRQF = (PF x PIE) + (AF x AIE) + (UF x UIE) + (WF x WIE) + (KF x KSE) + (RF x RIE)
BIT 6
BIT 6
PF
0
BIT 5
BIT 5
PF = PIE = 1
AF = AIE = 1
UF = UIE = 1
AF
0
IRQ
BAT
IRQ
pin goes low and a 1 appears in the IRQF bit. A read of Register
and V
pin is driven low. Flag bits PF, AF, and UF are cleared after
BIT 4
BIT 4
UF
0
BAUX
inputs.
WF = WIE= 1
KF = KSE= 1
RF = RIE = 1
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BIT 3
BIT 3
0
0
IRQ
pin. UF is cleared by reading Register C.
BIT 2
BIT 2
0
0
IRQ
signal is active and sets the
BIT 1
BIT 1
0
0
BIT 0
BIT 0
0
0
LSB
LSB