SIM800 Series_Multiplexer_Application Note_V1.04
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3 SIMCOM Multiplexer Protocol
SIMCom Multiplexer protocol provides a data transmission mechanism by establishing DLC between TE
and MS. Several DLC can be set up. Each one is independent to one another and has its own management
of buffer and flow control. All information transmitted between the TE and MS is conveyed in frames.
3.1 Transmission Frame Structures
The frame structure is composed of an opening and a closing flag, an address field, a control field, a Length
field, an information field and FCS field. Please see following table.
Opening
Flag
Address
Field
Control
Field
Length
Field
Information
Field
FCS
Field
Closing
Flag
1 byte
1 byte
1 byte
2 byte
Multi-byte
1 byte
1 byte
3.1.1 Opening and Closing Flag Field
Each frame begins and ends with a flag sequence octet which is defined as a constant bit pattern 0xF9.
3.1.2 Address Flag Field
The address field consists of a single octet. It contains the Data Link Connection Identifier (DLCI), the C/R
bit and the address field extension bit (EA) as following table.
Bit
1
2
3
4
5
6
7
8
EA
CR
DLCI
DLCI
DLCI
DLCI
DLCI
DLCI
The range of the address field may be extended by use of the EA bit. When the EA bit is set to 1 in an octet,
it signifies that this octet is the last octet of the address field. When the EA bit is set to 0, it signifies that
another octet of the address field follows. SIMCom multiplexer only supports one address octet so the EA
bit is always set to 1.
