AS260 datasheet(30/45 Pages) ONSEMI

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AR0260 DS Rev. G Pub. 4/15 EN

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Hardware Functions

Message Byte

Message bytes are used for sending register addresses and register write data to the slave

device and for retrieving register read data. The protocol used is outside the scope of the

two-wire serial interface specification.

Acknowledge Bit

Each 8-bit data transfer is followed by an acknowledge bit or a no-acknowledge bit in the

SCLK clock period following the data transfer. The transmitter (which is the master when

writing, or the slave when reading) releases SDATA. The receiver indicates an acknowl-

edge bit by driving SDATA LOW. As for data transfers, SDATA can change when SCLK is

LOW and must be stable while SCLK is HIGH.

No-Acknowledge Bit

The no-acknowledge bit is generated when the receiver does not drive SDATA low during

the SCLK clock period following a data transfer. A no-acknowledge bit is used to termi-

nate a read sequence.

Stop Condition

A stop condition is defined as a LOW -to-HIGH transition on SDATA while SCLK is HIGH.

Typical Serial Transfer

A typical read or write sequence begins by the master generating a start condition on the

bus. After the start condition, the master sends the 8-bit slave address/data direction

byte. The last bit indicates whether the request is for a read or a write, where a “0” indi-

cates a write and a “1” indicates a read. If the address matches the address of the slave

device, the slave device acknowledges receipt of the address by generating an acknowl-

edge bit on the bus.

If the request was a write, the master then transfers the 16-bit register address to which a

write should take place. This transfer takes place as two 8-bit sequences and the slave

sends an acknowledge bit after each sequence to indicate that the byte has been

received. The master then transfers the data as an 8-bit sequence; the slave sends

acknowledge bit at the end of the sequence. After 8 bits have been transferred, the slave’s

internal register address is automatically incremented, so that the next 8 bits are written

to the next register address. The master stops writing by generating a (re)start or stop

condition.

If the request was a read, the master sends the 8-bit write slave address/data direction

byte and 16-bit register address, just as in the write request. The master then generates a

(re)start condition and the 8-bit read slave address/data direction byte, and clocks out

the register data, 8 bits at a time. The master generates an acknowledge bit after each 8-

bit transfer. The slave’s internal register address is automatically incremented after every

8 bits are transferred. The data transfer is stopped when the master sends a no-acknowl-

edge bit.

Note:

If a customer is using direct memory writes (XDMA), AND the first write ends on an

odd address boundary AND the second write starts on an even address boundary

AND the first write is not terminated by a STOP, the write data can become corrupted.

To avoid this, ensure that a serial write is terminated by a STOP.

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