FOR AUTOMOTIVE 105°C OPERATION 2-WIRE REAL-TIME CLOCK

S-35390A H Series

Seiko Instruments Inc.

18



Power-on Detection Circuit and Register Status

The power-on detection circuit operates by power-on the S-35390A H Series, as a result each register is cleared; each

register is set as follows.

Real-time data register:

00 (Y), 01 (M), 01 (D), 0 (day of the week), 00 (H), 00 (M), 00 (S)

Status register 1:

"01h"

Status register 2:

"80h"

INT1 register:

"80h"

INT2 register:

"00h"

Clock correction register:

"00h"

Free register:

"00h"

"1" is set in the POC flag (B0 in the status register 1) to indicate that power has been applied. To correct the oscillation

frequency, the status register 2 goes in the mode the output of user-set frequency, so that 1 Hz clock pulse is output from

the

1

INT

pin. When "1" is set in the POC flag, be sure to initialize. The POC flag is set to "0" due to initialization so that

the output of user-set frequency mode is cleared (Refer to " Register Status After Initialization").

For the regular operation of power-on detection circuit, as seen in Figure 20, the period to power-up the S-35390A H

Series is that the voltage reaches 1.3 V within 10 ms after setting the IC’s power supply voltage at 0 V. When the power-on

detection circuit is not working normally is; the POC flag (B0 in the status register 1) is not in "1", or 1 Hz is not output from

the

1

INT pin. In this case, power-on the S-35390A H Series once again because the internal data may be in the indefinite

status.

Moreover, regarding the processing right after power-on, refer to " Flowchart of Initialization and Example of

Real-time Data Set-up

".

Within 10 ms

1.3 V

0 V

*1

*1.

0 V indicates that there are no potential differences between the VDD

pin and VSS pin of S-35390A H Series.

Figure 20 How to Raise the Power Supply Voltage