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Data / Commands multiplexing protocol
Introduction
The multiplexing protocol operates between a DCE (Data Communication Equipment:
the product) and a DTE (Data Terminal Equipment). It allows a double session over a
serial link interface: one for AT commands and one for DATA communications.
AT+WMUX=1 activates the Multiplexing Mode.With this mode, AT commands and
DATA are encapsulated into packets.The header of these packets allows to recognize
whether it is a DATA packet or an AT command packet. AT+WMUX=0 deactivates the
Multiplexing Mode and gets the product back to the default mode.This chapter presents
how the multiplexing mode handles the DATA and the AT commands flow. It also
describes the format of DATA packets and AT command packets.
AT command packets
An AT command is encapsulated into a packet with a header which allows to separate it
from DATA packets.This packet is formed by a header (3 bytes), the AT command itself
and a checksum (1 byte):
Start pattern 0xAA
..........................................................................................................................
Bit 0-7
AT command length LSB
............................................................................................................
Bit 0-7
AT command length MSB / AT command pattern, 0x1D
......................
Bit 0-2/ Bit 3-7
AT command
.........................................................................................................................................
Bit 0-7
Checksum
...................................................................................................................................................
Bit 0-7
The 3 bytes of the header are:
• the first byte (0xAA) is used to identify the packet,
• the second byte represents the 8 LSB (Low Significant Bits)
bits of the length of the AT command,
• the third byte is made of 2 parts :
• the 3 LSB bits are the 3 MSB (Most Significant Bits) bits of the length
of the AT command,
• the 5 MSB bits (0x1D which equals to 0xE8 with the 3 bits offset)
are used to identify an AT command.
The maximum length of an AT command could be 2047 bytes which is greater than all
the existing AT commands.
The checksum is the addition (modulo 256) of all the transmitted bytes (header bytes
and AT command bytes).
Содержание GD-01 TCP
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