L99LD21 datasheet(29/73 Pages) STMICROELECTRONICS

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DS11130 Rev 5

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L99LD21

SPI functional description

5.1

SPI protocol

ST-SPI is a standard used in ST automotive ASSP devices. SPI protocol standardization

here described defines a common structure of the communication frames and defines

specific addresses for product and status information.

The ST-SPI will allow usage of generic software to operate the devices while maintaining

the required flexibility to adapt it to the individual functionality of a particular product. In

addition to that, fail safe mechanisms are implemented to protect the communication from

external influence and wrong or unwanted usage.

5.2

SPI communication

At the beginning of each communication the master can read the content of the <SPI Mode>

length (32 bit) and the availability of additional features.

Each communication frame consists of a command byte which is followed by 3 data bytes.

The data returned on SDO within the same frame always starts with the <Global Status

Byte>. It provides general status information about the device. It is followed by 3 data bytes

(i.e. “in-frame-response”).

For write cycles the <Global Status Byte> is followed by the previous content of the

addressed register.

Table 5. Command byte (8 bit)

Operating code

Address

Bit

313029

2827

2524

Name

OC1

OC0

Table 6. Data byte 2

Data byte 2

Bit

2322212019181716

Name

D23

D22

D21

D20

D19

D18

D17

D16

Table 7. Data byte 1

Data byte 1

Bit

15141312

Name

D15

D14

D13

D12

D11

D10

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