DS1744 Maxim, DS1744 Datasheet - Page 5

• Manufacturer Part Number: DS1744
• Description: The DS1744 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) and 32k x 8 NV SRAM
• Manufacturer: Maxim

Table 1. Truth Table
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 DS1744 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 can 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 (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 toggles at 512Hz. When the seconds
register is being read, the DQ0 line toggles at the 512Hz 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 (DIP MODULE)
The DS1744 is guaranteed to keep time accuracy to within 1 minute per month at +25C. The RTC is
calibrated at the factory by Maxim using nonvolatile tuning elements, and 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; caution should be taken to place the RTC in the
lowest-level EMI section of the PC board layout. For additional information, refer to Application Note 58:
Crystal Considerations with Dallas Real-Time Clocks.
CLOCK ACCURACY (PowerCap MODULE)
The DS1744 and DS9034PCX are individually tested for accuracy. Once mounted together, the module
typically keeps time accuracy to within 1.53 minutes per month (35ppm) at +25°C. 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 PC board layout. For additional information, refer to Application Note 58:
Crystal Considerations with Dallas Real-Time Clocks.
V
V
SO
CC
V
< V
< V
CC
V
> V
CC
CC
SO
< V
< V
PF
PF
PF
V
CE
V
V
V
X
X
IH
IL
IL
IL
V
OE
V
X
X
X
X
IL
IH
WE
V
V
V
X
X
X
DS1744/DS1744P Y2K-Compliant, Nonvolatile Timekeeping RAMs
IH
IH
IL
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Deselect
Deselect
Deselect
MODE
Write
Read
Read
Data Out
High-Z
Data In
High-Z
High-Z
High-Z
DQ
Data-Retention Mode
CMOS Standby
POWER
Standby
Active
Active
Active