DS1307 64 x 8, Serial, I

2C Real-Time Clock

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OSCILLATOR CIRCUIT

The DS1307 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or

capacitors to operate. Table 1 specifies several crystal parameters for the external crystal. Figure 1 shows a

functional schematic of the oscillator circuit. If using a crystal with the specified characteristics, the startup time is

usually less than one second.

CLOCK ACCURACY

The accuracy of the clock is dependent upon the accuracy of the crystal and the accuracy of the match between

the capacitive load of the oscillator circuit and the capacitive load for which the crystal was trimmed. Additional

error will be added by crystal frequency drift caused by temperature shifts. External circuit noise coupled into the

oscillator circuit may result in the clock running fast. Refer to Application Note 58: Crystal Considerations with

Dallas Real-Time Clocks for detailed information.

Table 1. Crystal Specifications*

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Nominal Frequency

fO

32.768

kHz

Series Resistance

ESR

45

k

Ω

Load Capacitance

CL

12.5

pF

*The crystal, traces, and crystal input pins should be isolated from RF generating signals. Refer to

Application Note 58: Crystal Considerations for Dallas Real-Time Clocks for additional specifications.

Figure 2. Recommended Layout for Crystal

RTC AND RAM ADDRESS MAP

Table 2 shows the address map for the DS1307 RTC and RAM registers. The RTC registers are located in address

locations 00h to 07h. The RAM registers are located in address locations 08h to 3Fh. During a multibyte access,

when the address pointer reaches 3Fh, the end of RAM space, it wraps around to location 00h, the beginning of

the clock space.

NOTE: AVOID ROUTING SIGNAL LINES IN THE CROSSHATCHED

AREA (UPPER LEFT QUADRANT) OF THE PACKAGE UNLESS

THERE IS A GROUND PLANE BETWEEN THE SIGNAL LINE AND THE

DEVICE PACKAGE.

LOCAL GROUND PLANE (LAYER 2)

CRYSTAL

X1

X2

GND