Product manual

TAC Xenta Server – Gateway, Technical Manual B Protocols
Schneider Electric Buildings AB, June 2011 129 (184)
04-00124-06-en
B.2.2 Modbus Slave Devices
The Modbus Slave interface is added into the network pane of
XBuilder, as shown for an XLink example network in the following
screenshot.
Interface Properties
• Port Type – In most cases the RS-485 port option will be selected.
The RS-232 option may be suitable for connecting directly to a
master or simulator, but RS-485 will be required if additional slave
devices are attached to the Modbus serial line.
• Baud Rate, Parity, #Data Bits, #Stop Bits – All the communica-
tion parameters, such as baud rate and parity, must be the same for
all devices on the network.
• Framing Mode – Allows the applicable Modbus framing mode to
be selected (RTU or ASCII). Most Modbus networks use RTU
mode, which is a compact binary form suitable for local area net-
works. The ASCII mode is less compact because it uses 2 charac-
ters per byte, but may be better suited to wider area networks (such
as through modems).
Interface Status Signals
The Modbus Slave interface driver generates several network specific
communication status signals, as described below.
• ComsFail – Flags a complete communications failure. Activated
only if there is no detectable communications with the Modbus
master. Normally caused by incorrect communication property
settings, or by faulty wiring of the RS-485 network between the
Xenta 913 and the master.
• WdogTgl – Toggles state periodically. May be used by the control
system to check that the interface to the external master is operat-
ing.
• WdogFail – Indicates that at least one I/O signal has been defined
as “Toggled” but is not being updated by the master at the required
rate. Normally indicates that, although the master is connected and
communicating, either it or the interface is incorrectly configured
and so essential values are not being exchanged.