S35390A datasheet(36/51 Pages) SII

36 / 51 page

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

S-35390A H Series

Rev.2.2_00

Seiko Instruments Inc.



Reset After Communication Interruption

In case of communication interruption in the S-35390A H Series, for example, if the power supply voltage drops and only

the master device is reset during communication, the S-35390A H Series does not perform the next operation because the

internal circuit keeps the status prior to communication interruption. Since the S-35390A H Series does not have a reset

pin, users usually reset its internal circuit by inputting a stop condition. However, if the SDA is outputting "L" (during output

of acknowledgment signal or reading), the S-35390A H Series does not accept a stop condition from the master device. In

this case, users are necessary to finish acknowledgment output or reading of the SDA. Figure 45 shows how to reset.

First, input a start condition from the master device (the S-35390A H Series cannot detect a start condition because the

SDA in the S-35390A H Series is outputting "L"). Next, input a clock pulse equivalent to 7-byte data access (63-clock) from

the SCL. During this period, release the SDA line for the master device. By this procedure, SDA I/O before communication

interruption is finished, and the SDA line in the S-35390A H Series is released. After that, inputting a stop condition resets

the internal circuit and restores the regular communication. This reset procedure is recommended to be executed at

initialization of the system after the master device's power supply voltage is raised.

If this reset procedure is executed when the S-35390A H Series outputs an acknowledgment signal of a writing instruction,

the writing operation may be performed at the corresponding register, so caution should be exercised.

Start

condition

Stop

condition

Clocks equivalent to 7-byte data access

SCL

"L"

"L" or High-Z

High-Z

SDA

(Master device

output)

SDA

(S-35390A

H Series

output)

SDA

"L" or High-Z

"L"

Figure 45 How to Reset

S35390A Datasheet(PDF) 36 Page - Seiko Instruments Inc