DS1746 Maxim, DS1746 Datasheet - Page 5

• Manufacturer Part Number: DS1746
• Description: The DS1746 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) and 128k x 8 nonvolatile static RAM
• 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 one, like the
read bit, halts updates to the DS1746 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 zero 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 one 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 (DIP MODULE)
The DS1746 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. The
electrical environment also affects clock accuracy 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.
CLOCK ACCURACY (PowerCap MODULE)
The DS1746 and DS9034PCX are each individually tested for accuracy. Once mounted together, the
module will typically keep time accuracy to within ±1.53 minutes per month (35 ppm) at 25°C. The
electrical environment also affects clock accuracy 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.
V
V
SO
CC
V
<V
<V
CC
V
>V
CC
CC
SO
<V
<V
PF
PF
PF
V
V
V
V
CE
X
X
IH
IL
IL
IL
V
OE
V
X
X
X
X
IL
IH
WE
V
V
V
X
X
X
IL
IH
IH
Deselect
Deselect
Deselect
MODE
Write
Read
Read
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Data Out
High-Z
Data In
High-Z
High-Z
High-Z
DQ
Data-Retention Mode
CMOS Standby
POWER
Standby
Active
Active
Active