DS1338 I

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OPERATION

The DS1338 operates as a slave device on the serial bus. Access is obtained by implementing a START condition

and providing a device identification code, followed by data. Subsequent registers can be accessed sequentially

diagram (Figure 3) shows the main elements of the DS1338.

An enable bit in the seconds register controls the oscillator. Oscillator startup times are highly dependent upon

crystal characteristics, PC board leakage, and layout. High ESR and excessive capacitive loads are the major

contributors to long start-up times. A circuit using a crystal with the recommended characteristics and proper layout

usually starts within 1 second.

POWER CONTROL

The power-control function is provided by a precise, temperature-compensated voltage reference and a

registers are reset to 01/01/00 01 00:00:00 (MM/DD/YY DOW HH:MM:SS). The CH bit in the seconds register will be set

to a 1.

Table 1. Power Control

SUPPLY

CONDITION

READ/WRITE

ACCESS

POWERED

BY

No

No

Yes

Yes

OSCILLATOR CIRCUIT

The DS1338 uses an external 32.768kHz crystal. The oscillator circuit does not require any external resistors or

capacitors to operate. Table 2 specifies several crystal parameters for the external crystal. Figure 3 shows a

functional schematic of the oscillator circuit. The startup time is usually less than 1 second when using a crystal

with the specified characteristics.

PARAMETER

SYMBOL

MIN

TYP

MAX

UNITS

Nominal Frequency

32.768

kHz

Series Resistance

ESR

50

k



Load Capacitance

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.