Specifications

Chapter 4 – Serial Interface Control Commands
Multi-Tech Systems, Inc. AT Commands for EDGE (E1) Modems (S000474A) 67
4.6 AT+IFC Flow Control
Description: This command controls the flow control mode separately for each data direction (send and
receive). In contrast to this, flow control settings made with AT\Q are identical for both directions.
AT+IFC and the AT\Q are designed to configure only the TA. The TE must also be configured.
When programming the TE, bear in mind that the flow control mode set on the TA must be
compliant with the flow control method set on the TE. See notes below.
Syntax: Test Command: AT+IFC=?
Responses: +IFC: (list of supported <TEflowcontrol>s), (list of supported <TAflowcontrol>s)
OK
Read Command: AT+IFC?
Responses: +IFC: <TEflowcontrol>, <TAflowcontrol>
OK
Write Command: AT+IFC=<TEflowcontrol>, <TAflowcontrol>
Responses: OK
ERROR
+CME ERROR:<err>
Parameters:
<TEflowcontrol> Specifies the method used by the TA when sending data to the TE.
The value can be stored with AT&W.
0 none. Default (This is the default value if the parameter is omitted. It is also the
factory default value and can be restored to 0 with AT&F)
1 XON/XOFF − Local setting on the TA. Terminates flow control in the TA and,
thus, causes the TA to stop sending data to the remote TA.
2 RTS line − Local setting on the TA.
3 XON/XOFF − Used to evaluate flow control in the TA. If the data flow from the
TA requires that the transmission be stopped, the TE inserts the XON/OFF
control characters into the data stream to be sent, over the air, to the opposite
TE. It is the responsibility of the receiving TE to recognize and filter out from
the data stream the XON/OFF control characters. So, both TEs must have
XON/OFF flow control enabled.
Also, the receiving TA must be configured to use software flow control. This
means, that if the sending TA is configured for AT+IFC=3,x the receiving TA
must be set to AT+IFC=y,1. In addition, XON/OFF flow control must be
enabled on either TE.
If the TAs and TEs on both sides are properly configured, the transmission of
the XON/OFF control characters will instantly stop the data flow. So, value "3"
has an immediate effect on the over-the-air connection between both TEs.
<TAflowcontrol> Specifies the method used by the TA when receiving data from the TE.
The value can be stored with AT&W. The value can be displayed with AT&V.
0 None. Default (This is the default value if the parameter is omitted. It is also the
factory default value and can be restored to 0 with AT&F)
1 XON/XOFF
2 CTS line
Notes:
• If using XON/XOFF flow control (AT+IFC=1,x or AT+IFC=3,x) in data mode, +++ should not be used while
the data transmission is paused with XOFF. Before entering the command mode with +++ the paused
transmission should be resumed using the XON character.
• AT
+IFC and AT\Q usage influence each other; i.e., settings made with AT\Q apply to AT+IFC and, vice
versa, AT+IFC changes the AT\Q setting.
• Bear in mind that when you set a flow control method for one direction on the TA (with AT+IFC) the TE must
also be configured accordingly.
• The values "1" and "2" have only local effect for the connection between TA and TE. Value "3" has an
immediate effect on the over-the-air connection.
• XON/OFF flow control is not recommended for transferring binary files. This is because the data stream
might contain characters equal to the hex values typically used as XON/OFF control characters; i.e., values
11 (hex) resp. 17 (dec) and 13 (hex) resp. 19 (dec).
• This command is not PIN protected.
• This command is supported in airplane mode.