S35390A datasheet(30/51 Pages) SII

30 / 51 page

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

S-35390A H Series

Rev.2.2_00

Seiko Instruments Inc.



Serial Interface

The S-35390A H Series transmits / receives various commands via I

2C-bus serial interface to read / write data. Regarding

transmission is as follows.

1. Start condition

A start condition is when the SDA line changes "H" to "L" when the SCL line is in "H", so that the access starts.

2. Stop condition

A stop condition is when the SDA line changes "L" to "H" when the SCL line is in "H", and the access stops, so that the

S-35390A H Series gets standby.

tSU.STA

tHD.STA

tSU.STO

Start condition

Stop condition

SCL

SDA

Figure 32 Start / Stop Condition

3. Data transfer and acknowledgment signal

Data transmission is performed for every 1-byte, after detecting a start condition. Transmit data while the SCL line is in

"L", and be careful of spec of tSU.DAT and tHD. DAT when changing the SDA line. If the SDA line changes while the SCL

line is in "H", the data will be recognized as start / stop condition in spite of data transmission. Note that by this case,

the access will be interrupted.

During data transmission, every moment receiving 1-byte data, the devices which work for receiving data send an

acknowledgment signal back. For example, as seen in Figure 33, in case that the S-35390A H Series is the device

working for receiving data and the master device is the one working for sending data; when the 8th clock pulse falls,

the master device releases the SDA line. After that, the S-35390A H Series sends an acknowledgment signal back,

and set the SDA line to "L" at the 9th clock pulse. The S-35390A H Series does not output an acknowledgment signal

is that the access is not being done regularly.

Output acknowledgment

(Active "L")

tPD

Start condition

SCL

(S-35390A H Series

input)

SDA

(Master device

output)

SDA

(S-35390A H Series

output)

SDA is released

tSU.DAT

tHD.DAT

High-Z

Figure 33 Output Timing of Acknowledgment Signal

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