Serial-Port Flow Control (\Q) - Black Box 325 User Manual

MODEM 325 AND MODEM 325 CARD
6.14.4 S -P F
ERIAL ORT
Sets the type of flow control used by the serial port. If the serial-port speed exceeds that of the modem
connection, characters may be sent by the DTE to the modem faster than it can send them to the remote
modem. The modem holds characters in an internal buffer until they can be transmitted. When this
buffer is full, the modem uses flow control to cause the DTE to stop sending characters. As the modem
continues to transmit data and the buffer empties, flow control is again used to cause the DTE to resume
sending data.
AT\Q disables flow control.
When AT\Q1 is set, the modem generates and accepts XON/XOFF characters to start and stop the data
flow. These characters have the same parity as the DTE setup taken from the last AT command.
AT\Q2 allows use of CTS off to stop the data from the DTE and CTS on to restart it.
AT\Q3 forces the modem to act on CTS like \Q2. In addition, RTS on/off is used to start and stop data
from the modem to the DTE.
Command
\Q
\Q1
\Q2
\Q3
†default
6.14.5 XON/XOFF P
This option is active when flow control of the modem by the DTE has been selected for XON/XOFF and
the connect mode is reliable or normal. It enables or disables the sending of local flow control characters
(XON/XOFF) to the remote modem. In reliable mode, the modem treats incoming XON/XOFF
characters from the remote modem as data characters. In normal mode, the modem will look at the \G
command and act accordingly.
With \X1 in effect, local flow-control characters will be sent to the remote system. These
characters may turn on the flow of data from the remote system before the modem is ready
to receive more data, possibly resulting in a loss of data.
8 8
C (\Q)
LOW ONTROL
Table 6-49. Serial-Port Flow Control (\Q).
Operation
Disable DTE flow control
Enable XON/XOFF flow control†
Enable CTS flow control
Enable bilateral CTS/RTS flow control
(\X)
ASSTHROUGH
CAUTION