參數(shù)資料
型號(hào): DS1742-70
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: Timer or RTC
英文描述: 0 TIMER(S), REAL TIME CLOCK, PDIP24
封裝: 0.740 INCH, ENCAPSULATED, DIP-24
文件頁(yè)數(shù): 10/15頁(yè)
文件大小: 727K
代理商: DS1742-70
DS1742
4 of 15
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
DATA
ADDRESS
B
B
7
B
B
6
B
B
5
B
B
2
B
B
1
B
B
4
B
3
B
0
FUNCTION
RANGE
7FF
10 Year
Year
00–99
7FE
X
10
Month
01–12
7FD
X
10 Date
Date
01–31
7FC
BF
FT
X
Day
01–07
7FB
X
10 Hour
Hour
00–23
7FA
X
10 Minutes
Minutes
00–59
7F9
OSC
10 Seconds
Seconds
00–59
7F8
W
R
10 Century
Century
Control
00–39
OSC = STOP BIT
R = READ BIT
FT = FREQUENCY TEST
BF = BATTERY FLAG
W = WRITE BIT
X = SEE NOTE BELOW
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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