L99ASC03 datasheet(50/73 Pages) STMICROELECTRONICS

50 / 73 page

ST-SPI Protocol

L99ASC03

50/73

DocID023504 Rev 7

Data-in payload

The Payload is the data transferred to the slave device with every SPI communication

frame. The Payload always follows the OpCode and the Address bits.

For write accesses, the Payload represents the new data written to the addresses registers.

For Read & Clear operations, the Payload indicates the clear of a Status Register in case of

a '1' in the corresponding bit position.

For a Read Operation the Payload is not used. For functional safety reasons it is

recommended to set unused Payload to '0'.

4.2.2

SDO frame

The Data-Out Frame consist of 16 bits (GSB+Data).

The first eight transmitted bits contain device status information and are latched into the shift

transfer.

The subsequent byte contains the payload data and is latched into the shift register on the

eighth positive SCK edge. This could lead to an inconsistency of data between the GSB and

Payload due to different shift register load times. Anyhow, no unwanted Status Register

clear should appear, as status information should just be cleared with a dedicated bit clear

after read.

Figure 24. SDO frame

Data-out payload

The Payload is the data transferred from the slave device to the microcontroller with every

SPI communication frame. The Payload always follows the OpCode and the Address bits of

the frame that is currently being sent (In-Frame Response).

4.3

Addresses and data definition

4.3.1

Device information registers

The Device Information Registers can be read by using OpCode ‘11’. After shifting out the

GSB, the 8-bit payload is transmitted.

L99ASC03 Datasheet(PDF) 50 Page - STMicroelectronics