DS1742-100IND(2008) 查看數據表（PDF） - Maxim Integrated
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DS1742-100IND Datasheet PDF : 16 Pages
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DS1742
SETTING THE CLOCK
As shown in Table 2, bit 7 of the century register is the write bit. Setting the write bit to a 1, like
the read bit, halts updates to the DS1742 registers. The user can then load them with the
correct day, date and time data in 24-hour BCD format. Resetting the write bit to a 0 then
transfers those values to the actual clock counters and allows normal operation to resume.
STOPPING AND STARTING THE CLOCK OSCILLATOR
The clock oscillator may be stopped at any time. To increase the shelf life, the oscillator can be
turned off to minimize current drain from the battery. The OSC bit is the MSB (bit 7) of the
seconds registers, see Table 2. Setting it to a 1 stops the oscillator.
FREQUENCY TEST BIT
As shown in Table 2, bit 6 of the day byte is the frequency test bit. When the frequency test bit
is set to logic 1 and the oscillator is running, the LSB of the seconds register will toggle at 512
Hz. When the seconds register is being read, the DQ0 line will toggle at the 512 Hz frequency
as long as conditions for access remain valid (i.e., CE low, OE low, WE high, and address for
seconds register remain valid and stable).
CLOCK ACCURACY
The DS1742 is guaranteed to keep time accuracy to within ±1 minute per month at 25°C. Dallas
Semiconductor calibrates the RTC at the factory using nonvolatile tuning elements. The
DS1742 does not require additional calibration. For this reason, methods of field clock
calibration are not available and not necessary. Clock accuracy is also affected by the electrical
environment and caution should be taken to place the RTC in the lowest level EMI section of
the PCB layout. For additional information refer to Application Note 58.
Table 2. REGISTER MAP
ADDRES
DATA
S
B7B
B6B
B5B
B4B
B3B
7FF
10 Year
7FE
X
X
X
10
Month
7FD
X
X
10 Date
7FC
BF FT X
X
X
7FB
X
X
10 Hour
7FA
X
10 Minutes
7F9
OSC
10 Seconds
7F8
W
R
10 Century
FUNCTION
B2B
B1B
B0B
Year
Year
Month
Month
Date
Day
Hour
Minutes
Seconds
Century
Date
Day
Hour
Minutes
Seconds
Control
RANGE
00–99
01–12
01–31
01–07
00–23
00–59
00–59
00–39
OSC = STOP BIT
R = READ BIT
FT = FREQUENCY TEST
W = WRITE BIT
X = SEE NOTE BELOW
BF = BATTERY FLAG
Note: All indicated “X” bits are not used but must be set to “0” during write cycle to ensure proper clock operation.
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