SIM800 Series_Multiplexer_Application Note_V1.04
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3.6.4 MSC
MSC message frame is designed to convey virtual V.24 control signals. It has one mandatory control signal
byte and an optional break signal byte.
MSC shall be sent prior to any user data after a creation of a DLC.
Message format is:
Type
Length
DLCI
V.24 control signals
Break signals (Optional)
Message type coding octet:
1
2
3
4
5
6
7
8
EA
C/R
0
0
0
1
1
1
Hex value is 0xE3 (Command), 0xE1 (Response).
The EA bit is always set the 1.
The C/R bit is used to indicate if it is a Modem Status Command or Modem Status Response.
In a Modem Status Command it is the status of the sender’s own V.24 signals that shall be sent, but in a
Response it is copy of the V.24 signals that are received from the Command frame that shall be returned.
The DLCI field identifies the specific DLC to which the command applies. EA bit are always set to 1.
V.24 control signals format is:
1
2
3
4
5
6
7
8
EA
FC
RTC
RTR
reserved(0)
reserved (0)
IC
DV
Break signals is set to 0x01.
3.6.5 FCoff
Message type coding octet is:
1
2
3
4
5
6
7
8
EA
C/R
0
0
0
1
1
0
Hex value is 0x63 (Command), 0x61 (Response).
The length byte contains the value 0 and there are no value octets.