Rainbow Electronics DS17887 - Manual (Page 11)

DS17885/DS17887
11 of 38
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)
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 – 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
IRQ signal is active and sets 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
IRQ pin goes low and a 1 appears in the IRQF bit. A read of Register
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
IRQ pin. UF is cleared by reading Register C.
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 0 0 0 0 0 0
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
BAT
and V
BAUX
inputs.
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.