ISL12029 Intersil Corporation, ISL12029 Datasheet - Page 11
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ISL12029
Manufacturer Part Number
ISL12029
Description
Real Time Clock/Calendar
Manufacturer
Intersil Corporation
Datasheet
1.ISL12029.pdf
(28 pages)
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read by performing a sequential read. The read instruction
latches all Clock registers into a buffer, so an update of the
clock does not change the time being read. A sequential
read of the CCR will not result in the output of data from the
memory array. At the end of a read, the master supplies a
stop condition to end the operation and free the bus. After a
read of the CCR, the address remains at the previous
address +1 so the user can execute a current address read
of the CCR and continue reading the next Register.
Real Time Clock Registers (Volatile)
SC, MN, HR, DT, MO, YR: Clock/Calendar Registers
These registers depict BCD representations of the time. As
such, SC (Seconds) and MN (Minutes) range from 00 to 59,
HR (Hour) is 1 to 12 with an AM or PM indicator (H21 bit) or
0 to 23 (with MIL = 1), DT (Date) is 1 to 31, MO (Month) is 1
to 12, YR (Year) is 0 to 99.
DW: Date of the Week Register
This register provides a Day of the Week status and uses
three bits DY2 to DY0 to represent the seven days of the
week. The counter advances in the cycle 0-1-2-3-4-5-6-0-1-
2-… The assignment of a numerical value to a specific day
of the week is arbitrary and may be decided by the system
software designer. The default value is defined as ‘0’.
Y2K: Year 2000 Register
Can have value 19 or 20. As of the date of the introduction of
this device, there would be no real use for the value 19 in a
true real time clock, however.
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
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) (Volatile)
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).
Default
ADDR
003Fh
BAT
7
0
TABLE 1. STATUS REGISTER (SR)
AL1
6
0
AL0 OSCF
5
0
11
4
0
3
0
0
RWEL WEL
2
0
1
0
RTCF
0
1
ISL12029
BAT: Battery Supply
This bit set to “1” indicates that the device is operating from
V
hardware (ISL12029 internally). Once the device begins
operating from V
AL1, AL0: Alarm Bits
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.
OSCF: Oscillator Fail Indicator
This bit is set to “1” if the oscillator is not operating. The bit is
set to “0” only if the oscillator is functioning. This bit is read
only, and is set /reset by hardware.
RWEL: Register Write Enable Latch
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 nonvolatile 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
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 nonvolatile write cycle, so the device is ready
for the next operation immediately after the stop condition.
RTCF: Real Time Clock Fail Bit
This bit is set to a “1” after a total power failure. This is a
read only bit that is set by hardware (ISL12029 internally)
when the device powers up after having lost all power to
the device (both V
regardless of whether V
of only one of the supplies does not set the RTCF bit to “1”.
On power up after a total power failure, all registers are set
to their default states and the clock will not increment until
at least one byte is written to the clock register. The first
valid write to the RTC section after a complete power failure
resets the RTCF bit to “0” (writing one byte is sufficient).
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.
BAT
, not V
DD
. It is a read-only bit and is set/reset by
DD
DD
, the device sets this bit to “0”.
and V
DD
or V
BAT
BAT
go to 0V). The bit is set
is applied first. The loss
April 17, 2006
FN6206.4