LRI2K datasheet(30/89 Pages) STMICROELECTRONICS

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LRI2K protocol description

LRI2K

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LRI2K protocol description

The transmission protocol (or simply protocol) defines the mechanism used to exchange

instructions and data between the VCD and the LRI2K, in both directions. It is based on the

concept of "VCD talks first".

This means that an LRI2K will not start transmitting unless it has received and properly

decoded an instruction sent by the VCD. The protocol is based on an exchange of:

●

a request from the VCD to the LRI2K

●

a response from the LRI2K to the VCD

Each request and each response are contained in a frame. The frame delimiters (SOF,

EOF) are described in Section 6: LRI2K to VCD frames.

Each request consists of:

●

a request SOF (see Figure 9 and Figure 10)

●

flags

●

a command code

●

parameters, depending on the command

●

application data

●

a 2-byte CRC

●

a request EOF (see Figure 11)

Each response consists of:

●

an answer SOF (see Figure 24 to Figure 29)

●

flags

●

parameters, depending on the command

●

application data

●

a 2-byte CRC

●

an Answer EOF (see Figure 30 to Figure 35)

The protocol is bit-oriented. The number of bits transmitted in a frame is a multiple of eight

(8), i.e. an integer number of bytes.

A single-byte field is transmitted least significant bit (LSBit) first. A multiple-byte field is

transmitted least significant byte (LSByte) first, with each byte transmitted least significant

bit (LSBit) first.

The setting of the flags indicates the presence of the optional fields. When the flag is set (to

one), the field is present. When the flag is reset (to zero), the field is absent.

Table 7.

VCD request frame format

Request SOF Request Flags

Command

code

Parameters

Data

2 byte CRC

Request

EOF

Table 8.

LRI2K response frame format

Response

SOF

Response

Flags

Parameters

Data

2 byte CRC

Response

EOF

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