DS1647/DS1647P

Nonvolatile Timekeeping RAM

www.artschip.com

4

Table 1. Truth Table

Vcc

MODE

DQ

POWER

X

X

Deselect

High-Z

Standby

X

X

X

Deselect

High-Z

Standby

X

Write

Data In

Active

Read

Data Out

Active

Read

High-Z

Active

X

X

X

Deselect

High-Z

CMOS Standby

X

X

X

Deselect

High-Z

Data-Retention Mode

SETTING THE CLOCK

The MSB Bit, B7, of the control register is the write bit. Setting the write bit to a 1, like the read bit halts updates to the DS1647

registers. The user can them load them with the correct day, date and time data in 24-hour BCD format. Resetting the write 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

bit is the MSB for the second’s registers. Setting it to a 1 stops the oscillator.

FREQUENCY TEST BIT

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 second’s register will toggle at 512 Hz. When the seconds register is being read, the DQ0 line will toggle at the 512Hz

frequency as long as conditions for access remain valid (i.e.,

low,

low, and address for seconds register remain valid and

stable).

CLOCK ACCURACY (DIP MODULE)

The DS1647 is guaranteed to keep time accuracy to within ±1 minute per month at +25

℃. The RTC is calibrated at the factory by

ARTSCHIP Semiconductor 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 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 DS1647 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 (35ppm) at +25

℃. 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.