Westermo TD-22 - Manual (Page 43)

To use multidrop V23 in half duplex
Multidrop connection is possible only when the modem is set for V23 half duplex. This allows a
maximum line transmission speed to 1200 baud. The speed at the serial port can however be higher.
The carrier (the transmission) is activated with the RTS signal in the RS-232 interface and the
carrier remains high until the transmission buffer is empty.
The actual number of modems that can be multidropped depends on the line quality and the range is
dependant on the number of attached devices.
V23 half duplex is achieved by switching ON SW1:2 and SW5:2 and switching OFF the rest of SW1
and SW5.
Frequently used settings for PLC-systems
and industrial applications.
Most PLC-systems and other industrial applications require the same changes to the standard
settings.
The most commonly encountered problems concern speed, parity and control signals from the
connected equipment.
Speed and parity are changed with the switches under the cover in block SW4. If this action does not
solve the problem the modem’s answering codes and possible echoing of commands might be the
source of the difficulty. Here below follows a list of commands that might resolve the problems.
(The commands may of course be placed on one single command line if desired, as per the example1):
ATV0 Gives the answering codes in short format. (digits)
ATQ1 No result codes are sent on the RS-232 connection.
ATE0 Commands that are sent from the terminal/computer etc. are not echoed back
to the RS-232 connection.
AT&C1 DCD will follow the carrier on the line.
AT&K0 No handshaking.
AT&A1 Character abort option on.
For further information regarding these commands please refer to the specific section of this manual.
44 6177-2203