L99H92 datasheet(20/77 Pages) STMICROELECTRONICS

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The first two transmitted bits (MSB, MSB-1) contain the operation code, which represents the command/

instruction that will be performed. The following 6 bits (MSB-2 to MSB-7) represent the address on which the

command/operation will be performed.

The subsequent two bytes contain the payload.

Figure 15. SDI frame

GADG120920221006SA

OC1 OC0

OPCODE

ADDRESS

DATA Byte 2

DATA Byte 1

MSB

LSB

time

DATA Byte 3

time

Operating code

The operating code is used to distinguish between different commands/operations on registers of the slave

device.

Table 5. Operation codes

OC1

OC0

Description

Write command

Read command

Read & Clear command

Read device information command

Any Write command (with no parity error, no wrong address and no CLK count error) will modify the content of

the addressed control register with the payload. Besides this, a shift out of the content (data present at

Communication Start) of the addressed register is performed.

A Read command shifts out the data present in the addressed register at Communication Start. The payload

data is ignored, and the data of the addressed register will not be modified. Moreover, a Burst Read can be

performed.

A Read & Clear command (with no parity error, no wrong address and no CLK count error) 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’.

Besides this, a shift out of the content (data present at Communication Start) of the register is performed.

Note:

to avoid any loss of any reported status, it is recommended to clear just the status register bits, which are

already reported in the previous communication frame (Selective Bitwise Clear).

Advanced operation codes

Two Advanced Operation Codes can be used to set all control registers to the default value and to clear all status

registers by one single SPI frame respectively.

A ‘set all control registers to default’ command is launched when an SPI frame with OpCode ‘11’ and

address ’111111’ is sent to the device.

A ‘clear all status registers’ command is launched when an SPI frame with OpCode ‘10’ and address’111111’ is

sent to the device.

Data-in payload

The Payload (Data Byte 1 to Data Byte 2) is the data transferred to the device with every SPI communication. The

Payload always follows the OpCode and the Address bits.

L99H92

ST SPI 4.1

DS14069 - Rev 4

page 20/77

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