DS12C887
REGISTER C
MSB
BIT 7
BIT 6
PF
BIT 5
AF
BIT 4
UF
BIT 3
0
BIT 2
0
BIT 1
0
LSB
BIT 0
IRQF
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
i.e., IRQF = (PF
●
PIE) + (AF
●
AIE) + (UF
●
UIE)
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 or when the RESET pin is low.
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 1’s, the
IRQ
signal is active and will
set the IRQF bit. The PF bit is cleared by a software read of Register C or a RESET .
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 will go low and a 1 will appear in the IRQF bit. A RESET or 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 1 in UF causes the IRQF bit to be a 1, which will assert the
IRQ
pin. UF is cleared by reading
Register C or a RESET .
BIT 3 THROUGH BIT 0 -
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
0
BIT 5
0
BIT 4
0
BIT 3
0
BIT 2
0
BIT 1
0
LSB
BIT 0
VRT
0
VRT
- The Valid RAM and Time (VRT) bit indicates the condition of the battery connected to the V
BAT
pin. This bit is not writeable and should always be a 1 when read. If a 0 is ever present, an exhausted
internal lithium energy source is indicated and both the contents of the RTC data and RAM data are
questionable. This bit is unaffected by RESET
.
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.
9 of 19
DALLAS [ DALLAS SEMICONDUCTOR ]
