ISL12024IRTC Datasheet, PDF (9/24 Pages) Intersil Corporation – Real-Time Clock/Calendar

ISL12024IRTC
24 Hour Time
If the MIL bit of the HR register is 1, the RTC uses a 24-hour
format. If the MIL bit is 0, the RTC uses a 12-hour format,
and the H21 bit functions as an AM/PM indicator with a ‘1’
representing PM. The clock defaults to standard time with
H21 = 0.
Leap Years
Leap years add the day February 29 and are defined as
those years that are divisible by 4.
Status Register (SR)
The Status Register is located in the CCR memory map at
address 003Fh. This is a volatile register only, and is used to
control the WEL and RWEL write enable latches, read power
status and two alarm bits. This register is separate from both
the array and the Clock/Control Registers (CCR).
TABLE 1. STATUS REGISTER (SR)
ADDR 7
65
43
2
1
0
003Fh BAT AL1 AL0 0 0 RWEL WEL RTCF
Default 0
00
00
0
0
1
BAT: Battery Supply - Volatile
This bit set to “1” indicates that the device is operating from
V_BAT, not V_DD. It is a read-only bit and is set/reset by
hardware (ISL12024IRTCZ internally). Once the device
begins operating from V_DD, the device sets this bit to “0”.
AL1, AL0: Alarm Bits - Volatile
These bits announce if either alarm 0 or alarm 1 match the
real-time clock. If there is a match, the respective bit is set to
‘1’. The falling edge of the last data bit in a SR Read
operation resets the flags. (Note: Only the AL bits that are
set when an SR read starts will be reset). An alarm bit that is
set by an alarm occurring during an SR read operation will
remain set after the read operation is complete.
RWEL: Register Write Enable Latch Volatile
This bit is a volatile latch that powers up in the LOW
(disabled) state. The RWEL bit must be set to “1” prior to any
writes to the Clock/Control Registers. Writes to RWEL bit do
not cause a non-volatile write cycle, so the device is ready
for the next operation immediately after the stop condition. A
write to the CCR requires both the RWEL and WEL bits to be
set in a specific sequence.
WEL: Write Enable Latch - Volatile
The WEL bit controls the access to the CCR during a write
operation. This bit is a volatile latch that powers up in the
LOW (disabled) state. While the WEL bit is LOW, writes to the
CCR address will be ignored, although acknowledgment is
still issued. The WEL bit is set by writing a “1” to the WEL bit
and zeroes to the other bits of the Status Register. Once set,
WEL remains set until either reset to 0 (by writing a “0” to the
WEL bit and zeroes to the other bits of the Status Register) or
until the part powers up again. Writes to WEL bit do not cause
a non-volatile write cycle, so the device is ready for the next
operation immediately after the stop condition.
RTCF: Real-Time Clock Fail Bit - Volatile
This bit is set to a ‘1’ after a total power failure. This is a read
only bit that is set internally when the device powers up after
having lost all power to the device. The bit is set regardless
of whether V_DD or V_BAT is applied first. The loss of only one
of the supplies does not result in setting the RTCF bit. The
first valid write to the RTC after a complete power failure
(writing one byte is sufficient) resets the RTCF bit to ‘0’.
Unused Bits:
Bit 3 in the SR is not used, but must be zero. The Data Byte
output during a SR read will contain a zero in this bit location.
9
FN6749.1
December 15, 2011