DS1689 Datasheet, PDF (14/32 Pages) Dallas Semiconductor – 3-Volt/5-Volt Serialized Real-Time Clock with NV RAM Control

REGISTER C
MSB
BIT 7
BIT 6
IRQF
PF
BIT 5
AF
BIT 4
UF
BIT 3
0
BIT 2
0
DS1689/DS1693
BIT 1
0
LSB
BIT 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
AF = AIE = 1
UF = UIE = 1
WF = WIE = 1
KF = KSE = 1
RF = RIE = 1
i.e., IRQF = (PF · PIE) + (AF · AIE) + (UF · UIE) + (WF · WIE) + (KF · KSE) + (RF · RIE)
Any time the IRQF bit is a one, 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 which 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 will set
the IRQF bit. The PF bit is cleared by a software read of Register C.
AF - A one 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 will go low and a one will appear in the IRQF bit. A read of
Register C will clear 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 will assert the IRQ pin. UF is cleared by reading
Register C.
BIT 0 THROUGH BIT 3 - These are unused bits of the status Register C. These bits always read 0 and
cannot be written.
REGISTER D
MSB
BIT 7
BIT 6
VRT
0
BIT 5
0
BIT 4
0
BIT 3
0
BIT 2
0
BIT 1
0
LSB
BIT 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 THROUGH BIT 0 - The remaining bits of Register D are not usable. They cannot be written and,
when read, they will always read 0.
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