Rainbow Electronics DS1687 - Manual (Page 14)

DS1685/DS1687
14 of 38
REGISTER C
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
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 – 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. The PF bit is cleared by a software read of 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. A read of Register C clears
AF.
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. UF is 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
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 – The valid RAM and time (VRT) bit indicates the condition of the battery connected to the V
BAT
pin or the battery connected to V
BAUX
, whichever is at a higher voltage. This bit is not writable and should
always be a 1 when 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.