Specifications

Chapter 4 – Serial Interface Control Commands
Multi-Tech Systems, Inc. AT Commands for EDGE Modems (S000371B) 55
• The current setting of AT+IPR will be preserved when you download firmware or in the event of power failure.
Note: A firmware update does not restore the factory setting.
• Generally, AT+IPR should be used as a standalone command. If nethertheless combinations with other
commands on the same command line cannot be avoided, there are several constraints to be considered:
∗ Avoid combinations with the AT commands listed in Section 1.4.2, Combining AT commands on the same
command line.
∗ Take into account, that a delay of 100ms is required between the response to the last command (e.g., OK)
and the next command on the same line.
∗ When you enter AT+IPR=0, autobauding will be activated after the response to the last command is
received.
∗ When local echo is active (ATE1) and you enter AT+IPR=x with other commands you may encounter the
following problem: if switching to the new bit rate takes effect while a response is being transmitted, the last
bytes may be sent with the new bit rate and thus, not properly transmitted. The following commands will be
correctly sent at the new bit rate.
• In order to account for greater amounts of data it is recommended to choose a minimum bit rate of 2400 bps. If
the ME is operated in Multiplex mode we suggest a minimum bit rate of 4800bps.
• A selected bit rate takes effect after the write commands returns OK (except for Multiplex mode).
• In Multiplex mode, the write command AT+IPR=<rate> will not change the bit rate currently used, but the new bit
rate will be stored and becomes active, when the module is restarted.
4.9.1 Autobauding
To take advantage of autobaud mode specific attention must be paid to the following requirements:
• Synchronization between TE and TA.
Ensure that TE and TA are correctly synchronized and the bit rate used by the TE is detected by the TA. To allow
the bit rate to be synchronized simply use an “AT” or “at” string. This is necessary
∗ after you have activated autobauding
∗ when you start up the GSM engine while autobauding is enabled. It is recommended to wait 3 to 5 seconds
before sending the first AT character. Otherwise undefined characters might be returned.
If you want to use autobauding and autoanswer at the same time, you can easily enable the TE-TA
synchronization, when you activate autobauding first and then configure the autoanswer mode (ATS0 ≠’ 0).
• Restrictions on autobauding operation.
∗ The serial interface shall be used with 8 data bits, no parity and 1 stop bit (factory setting); e.g., 2 stop bits are
not supported for autobaud mode.
∗ The command A/ cannot be used.
∗ Only the strings “AT” or “at” can be detected (neither “At” nor “aT”).
∗ URCs that may be issued before the ME detects a new bit rate (by receiving the first AT character) will be sent
at the previously detected bit rate or, after ME restart, at 57600 bps.
∗ It is not recommended to switch to autobauding from a bit rate that cannot be detected by the the autobaud
mechanism (e.g., 300 bps). Responses to AT+IPR=0 and any commands on the same line might be corrupted.
∗ When autobauding is switched on: (DAR)
∗ only data length, parity, and baud rate are automatically detected.
∗ if using 1 stop bit, AT+ICF=1 should not be used because AT+ICF=1 uses 2 stop bits.
∗ if using 2 stop bits, no combination of AT_ICF should be used.
• Autobauding and bit rate after restart.
The most recently detected bit rate is stored when the ME is powered down (with AT^SMSO). Therefore, each time
the module is restarted the correct bit rate must be found as described above. Unless the bit rate is determined, the
following constraints apply:
∗ An incoming CSD call or a network initiated GPRS request cannot be accepted. This must be taken into
account when autobauding and autoanswer mode (ATS0 ≠’ 0) are enabled at the same time, especially if SIM
PIN 1 authentication is done automatically and the setting ATS0 ≠’ 0 is stored to the user profile with AT&W.
Until the bit rate is found, URCs generated after restart will be output at 57600 bps. This applies only to user
defined URCs, such as “+CREG”, “CCWA”, “^SCKS” etc. The URCs “^SYSSTART”, and "^SYSSTART
AIRPLANE MODE" will not be indicated when autobauding is enabled.
Note: To avoid any problems caused by undetermined bit rates in the direction from TA to TE we strongly
recommend to configure a fixed bit rate rather than autobauding.
• Autobauding and multiplex mode.
If autobauding is active, you cannot switch to multiplex mode.