DS1647/DS1647P

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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 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 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 512Hz. 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., CE low, OE 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°C. The RTC is

calibrated at the factory by Dallas 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°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.

Table 2. Register Map—BANK1

ADDRESS

DATA

FUNCTION

7FFFF

—

—

—

—

—

—

—

—

Year

00–99

7FFFE

X

X

X

—

—

—

—

—

Month

01–12

7FFFD

X

X

—

—

—

—

—

—

Date

01–31

7FFFC

X

FT

X

X

X

—

—

—

Day

01–07

7FFFB

X

X

—

—

—

—

—

—

Hour

00–23

7FFFA

X

—

—

—

—

—

—

—

Minutes

00–59

7FFF9

OSC

—

—

—

—

—

—

—

Seconds

00–59

7FFF8

W

R

X

X

X

X

X

X

Control

A

OSC

= STOP BIT

R = READ BIT

FT = FREQUENCY TEST

W = WRITE BIT

X = UNUSED

Note:

All indicated “X” bits are unused, but must be set to “0” when written to ensure proper clock operation.