LRI512 datasheet(16/54 Pages) STMICROELECTRONICS

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LRI512

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LRI512 PROTOCOL DESCRIPTION

The Transmission protocol defines the mecha-

nism to exchange instructions and data between

the VCD and the LRI512, in both directions.

It is based on the concept of “VCD talks first”.

This means that any LRI512 does not start trans-

mitting unless it has received and properly decod-

ed an instruction sent by the VCD.

The protocol is based on an exchange of

– a Request from the VCD to the LRI512

– a Response from the LRI512 to the VCD

Each Request and each Response is contained in

a Frame. The frame delimiters (SOF, EOF) are de-

scribed in the previous paragraphs.

Each Request consists of

– Request SOF (see Figure 9 and Figure 10)

– Flags

– A Command Code

– Parameters, depending on the Command

– Application data

– 2-byte CRC

– Request EOF (see Figure 11)

Each Response consists of

– Answer SOF (see Figure 20 to Figure 23)

– Flags

– Parameters, depending on the Command

– Application data

– 2-byte CRC

– Answer EOF (see Figure 24 to Figure 27)

The protocol is bit-oriented. The number of bits

transmitted in a frame is a multiple of eight (8) –

that is, an integer number of bytes.

A single-byte field is transmitted Least Significant

Bit (LSBit) first.

A multiple-byte field is transmitted Least Signifi-

cant Byte (LSByte) first, each byte is 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

Table 8. LRI512 Response Frame Format

Figure 29. LRI512 Protocol Timing

Request

SOF

Request Flags

Command Code

Parameters

Data

2 Bytes

CRC

Request

EOF

Response

SOF

Response

Flags

Parameters

Data

2 Bytes

CRC

Response

EOF

AI06830

VCD

Request Frame

(Table 7)

Request Frame

(Table 7)

LRI512

Response Frame

(Table 8)

Response Frame

(Table 8)

Timing

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