SX8722 datasheet(21/108 Pages) SEMTECH

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ACS - Revision 4.2

October 2008

www.semtech.com

Page 21

ADVANCED COMMUNICATIONS & SENSING

DATASHEET

SX8722

High gain acquisition for sensor interface

8. Serial communication

The serial interface is a read-write 2 wire slave device. The SCL wire carries the clock information and SDA carries the data.

The output drivers on the bus are open drain current sinks.

The SCL wire is controlled by the master on the bus. Since the SX8722 is fairly slow, it may stretch the low clock phase

when required. The SDA wire is controlled by the master or the slave depending on the operation.

SDA only changes while the clock signal is low except for the (repeated) start or stop conditions.

The (repeated) start condition for the transmission is a high to low transition on SDA while SCL is high. The stop condition is

a low to high transition while SCL is high.

To read data from the SX8722, the master has to send successively a start bit, the slave address, a write bit. If the slave

address corresponds to the address of the SX8722 and the preceding operation is completed, the SX8722 sends an

acknowledge bit. The master then sends the read command which is acknowledged by the salve, the memory address that

it would like to read which is also acknowledged by the slave. The master issues a repeated start, repeats the slave address

and read bit. The slave acknowledges and returns the data to the master. The master terminates the communication by a

"not acknowledge" and a stop bit.

To write data to the SX8722, the format is very similar. Only the data direction is different and the acknowledgement of the

slave after the data reception.

8.1. Write data direct

The diagram below shows the write operation.

Figure 7. I2C frame: write register, command 0x10

The diagram below shows the write operation at successive addresses (burst mode)

Figure 8. I2C frame: write burst register, command 0x10

SDA

DEVICE

ADDRESS

VALUE

COMMAND

SDA

DEVICE

ADDRESS

VALUE (n)

VALUE (n + x)

COMMAND

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