Specifications

Chapter 4 – Serial Interface Control Commands
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371B) 56
4.10 AT+CMUX Enter Multiplex Mode
Description: All information provided in this section applies to the ASC0 interface only.
Multiplex mode according to the ETSI TS 101 669 and GSM 07.10 enables one physical serial
asynchronous interface to be partitioned into three virtual channels. This allows you to take
advantage of up to 3 simultaneous sessions running on the serial interface. For example, you
can send or receive data or make a call on the first channel, while the other two channels are
free to control the module with AT commands.
The Multi-Tech wireless modem module incorporates an internal multiplexer and thus integrates
all the functions needed to implement full-featured multiplex solutions. For the application on top,
customers have the flexibility to create their own multiplex programs conforming to the
multiplexer protocol. To help system integrators save the time and expense of designing
multiplexer applications, contact Multi-Tech about a ready-to-use multiplex driver for Windows
2000 and Windows XP. Another approach is to develop customized solutions based on the
sources of the WinMux2k driver.
The WinMUX2k driver and its source files can be supplied on request. Please contact your local
distributor to obtain the latest installation software and user’s guide.
Test Command Syntax AT+CMUX=?
Response: +CMUX: (list of supported<mode>s)
OK
Read Command Syntax: AT+CMUX?
Response: +CMUX: <mode>
OK
ERROR
+CME ERROR: <err>
Write Command Synatx: AT+CMUX=<mode>
Response: OK
ERROR
+CME ERROR: <err>
Parameter Descriptions:
<mode>
Multiplexer transparency mechanism
0 Basic option
<subset>
Subparameters defined in GSM07.07 are adjusted for control and logical channels as follows 0 UIH frames used
only (control channel)
Notes:
• The write command is used to enter the multiplex mode. The setup of the logical channels is initiated by the TE;
i.e., the TE acts as initiator. This means that the TE shall ensure that logical channels are established before any
further actions on the channels can be started.
• There is a timeout of five seconds, if the multiplexer protocol is enabled and no multiplexer control channel is
established. The GSM engine returns to AT command mode.
• The parameter maximum frame size (N1) of AT+CMUX in GSM 07.10 is fixed to 98 bytes and cannot be
changed. All other parameters are not available.
• Multiplexer mode requires character framing to be set to 8 bits, no parity, and 1 stop bit. The settings can be
using AT+ICF=3.
4.10.1 Restrictions on Multiplex Mode
When the serial interface ASC0 is in multiplex mode, data and fax calls can only be set up on logical channel 1.
Due to this restriction, AT commands have a different behavior on channels 2+3 compared to channel 1. Several
commands are not available, others return different responses. This section summarizes the concerned commands.