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W&T
5.4.15 &K (AT&K[0|3|4|5|6])
Flow control
Default setting: 3 = RTS/CTS
This command determines the flow control between the LAN-
Modem and the connected serial device:
• &K0
(no handshake)
Flow control is turned off. The LAN-Modem sends all data
to the serial device regardless of the status of the hands-
hake input RTS. In the opposite direction the LAN-Modem
has no way to report an impending overflow of its input
buffer through the CTS output, so that in this case the serial
applications are responsible for ensuring data integrity.
• &K3
(RTS/CTS)
Flow control is handled by the port signals RTS and CTS.
The LAN-Modem sends serial data only when there is an
enable level on its RTS input. An impending overflow of the
serial input buffer is signaled by the CTS output.
• &K4
(Xon/Xoff)
Flow control is handled by the control characters Xon (hex
11) and Xoff (hex 13), whereby these characters are filtered
out from the user data stream. If the LAN-Modem receives
an Xoff, no additional data are sent to the serial device until
the latter has sent an Xon. The LAN-Modem indicates its rea-
dy or not-ready status likewise using an Xoff or Xon.
• &K5
(transparent Xon/Xoff)
As in the case of &K4 the flow control is handled by Xon/
Xoff. The control characters are now however not filtered
out, but rather sent transparent to the communication
partner.
• &K6
(RTS/CTS + Xon/Xoff)
Flow control is handled by RTS/CTS and Xon/Xoff. The
modem generates signals for both handshake procedures
and allows itself to be prevented from continuing to send
by means of Xoff or a returned RTS.
Subject to error and alteration
Modem Operation
57
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