Functions
INSYS GSM small 2.0
11.6
Data Flow Control (Handshake)
The data flow control ensures that the data transfer is interrupted as soon as the
modem buffer exceeds a certain level. Two data flow control options are available:
Via the control lines RTS and CTS, or via the control characters XON/XOFF which
are inserted into the data stream.
11.6.1
Hardware Data Flow Control (RTS/CTS)
The hardware data flow control works in two directions. When the critical buffer
level is exceeded, the modem will set the CTS line to "low" and will thus indicate to
the application to interrupt the data flow. When the buffer is emptied sufficiently
for the INSYS GSM small 2.0 to be able to receive data again, the CTS line is set to
"high". Reversely, the application can also indicate to the INSYS GSM small 2.0 to
hold the data flow. This is done via the RTS line. If it is set to "low", the modem will
hold the data flow to the application. The application will set it to "high" to request
data from the INSYS GSM small 2.0.
The data flow control with RTS/CTS behaviour is enabled by default.
Configuration with HSComm
Select the type of data flow control or switch it off completely on the
"Serial interface" tab in the "Handshake" panel.
Configuration with AT commands
In order to enable data flow control and set
the type to RTS/CTS, use the command
AT\Q3
In order to disable data flow control, use
the command
AT\Q0
11.6.2
Software Data Flow Control (XON/XOFF)
When the input buffer of the modem exceeds a certain fill state, the modem will
insert an XOFF character into the data stream to the application. This character will
cause the application to send no more data. It will depend on the according appli-
cation software if the XON/XOFF data flow control is supported.
After the input buffer of the modem is emptied enough that data can be received
again, the modem will send an XON character to the application. This character will
cause the application to send data to the modem again. Analogously, the applica-
tion can insert XON/XOFF characters into the data stream to switch the data flow
on and off. The XON/XOFF data flow control is only available when the transmitted
data do not contain the characters XON or XOFF, which usually appear only in ac-
tual ASCII texts (7 bit). When binary data (programs, etc.) are transmitted, or in the
XMODEM transmission protocol, for example, occasionally appearing XON or
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