L99ASC03 datasheet(48/73 Pages) STMICROELECTRONICS

48 / 73 page

ST-SPI Protocol

L99ASC03

48/73

DocID023504 Rev 7

Figure 23. SDI frame

Operating codes

The operating code is used to distinguish between different access modes to the registers of

the slave device.

A Write Operation writes the payload data to the addressed register if a write access is

allowed (e.g. Control Register, valid data). In addition, the content of the addressed register

(the data present at Communication Start) is shifted out on the SDO pin.

A Read Operation shifts out the data present in the addressed register at Communication

Start. The payload data is ignored and internal data are not modified. In addition a Burst

Read can be performed.

A Read & Clear Operation will lead to a clear of addressed status bits. The bits to be cleared

are defined first by address, second by payload bits set to ‘1’. In addition, the content of the

addressed register (the data present at Communication Start) is shifted out on the SDO pin.

Status registers that change their status during a communication frame could be cleared by

an ongoing Read & Clear Operation and would be reported neither in the ongoing

communication frame nor in the next communication frame. To avoid missing information

about any status change, it is recommended to clear the status bits that have been already

reported in previous communication frames (Selective Bitwise Clear).

Address

Following the OpCode bits, the six Address bits are a fixed part of the communication frame.

The six bits, in combination with the OpCode, allow access to a 2 x 64-wide address range.

Table 31. Operation codes

OC1

OC0

Description

Write operation

Read operation

Read & Clear operation

Read Device information

L99ASC03 Datasheet(PDF) 48 Page - STMicroelectronics