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M24LR64-R protocol description

M24LR64-R

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Doc ID 15170 Rev 14

M24LR64-R protocol description

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

instructions and data between the VCD and the M24LR64-R, in both directions. It is based

on the concept of “VCD talks first”.

This means that an M24LR64-R 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 M24LR64-R

●

a response from the M24LR64-R to the VCD

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

EOF) are described in Section 12: M24LR64-R to VCD frames.

Each request consists of:

●

a request SOF (see Figure 20 and Figure 21)

●

flags

●

a command code

●

parameters, depending on the command

●

application data

●

a 2-byte CRC

●

a request EOF (see Figure 22)

Each response consists of:

●

an answer SOF (see Figure 35 to Figure 40)

●

flags

●

parameters, depending on the command

●

application data

●

a 2-byte CRC

●

an answer EOF (see Figure 41 to Figure 46)

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 significant 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 20.

VCD request frame format

Request SOF Request_flags

Command

code

Parameters

Data

2-byte CRC

Request

EOF

Table 21.

M24LR64-R Response frame format

Response

SOF

Response_flags

Parameters

Data

2-byte CRC

Response

EOF

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