Specifications

SIM900 AT Command Manual

SIM900_AT Command Manual_V1.03 42 12/24/2010

Reference

V.25ter

Note

Factory setting is AT+IPR=0（auto-bauding）.

2.2.41.1 Auto-bauding

Synchronization between DTE and DCE ensure that DTE and DCE are correctly synchronized and

the baud rate used by the DTE is detected by the DCE (= ME). To allow the baud rate to be

synchronized, simply issue an "AT" string. This is necessary when you start up the module while

auto-bauding 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 auto-bauding and auto-answer at the same time, you can easily enable the

DTE-DCE synchronization, when you activate auto-bauding first and then configure the

auto-answer mode.

Restrictions on auto-bauding operation

z The serial interface has to be operated at 8 data bits, no parity and 1 stop bit (factory

setting).

z Only the strings

"AT" or "At" (not "aT" or "at") can be detected when auto-bauding is

enabled.

z AT+IPR=0 setting to auto-bauding will take effect after module resets. If user wants to

change DTE baud rate during module is running, i.e. from 57600 to 4800, DTR shall be

used to urge auto-bauding progress. DTR shall be pulled up to invalid state at least 2

seconds by DTE and then pulled down to valid state. The step will urge auto-bauding

progress and DCE will synchronize its baud rate after it receives data from the serial port.

z Unsolicited Result Codes that may be issued before the ME detects the new baud rate (by

receiving the first AT Command string) will be sent at the previously detected baud rate.

z The Unsolicited Result Codes

"RDY" and so on are not indicated when you start up the ME

while auto-bauding is enabled.

z It is not recommended to switch to auto-bauding from a baud rate that cannot be detected

by the auto-bauding mechanism (e.g. 300 baud). Responses to +IPR=0 and any commands

on the same line might be corrupted.

Auto-bauding and baud rate after restart

The most recently detected baud rate can not be stored when module is powered down.

2.2.42 AT+HVOIC Disconnect Voice Call Only

AT+HVOIC Disconnect Voice Call Only

Execution

Command

AT+HVOIC

Response

Disconnect existing voice call by local TE from Command line and

terminate call with existing PPP or CSD connection on.

Reference

V.25ter

Note