Rockwell Automation T8xxx Trusted Communications Interface - Manual (Page 26)

Trusted
TM
Communication Interface T8151B
Issue 21 Apr 10 PD-T8151B 26
3.5.3. Broadcast Tab
Figure 7 Modbus Master Broadcast Configuration
The Modbus broadcast mode is supported by the Modbus Master. The Modbus broadcast is an
unacknowledged write data message sent from the master using slave ID 0. All slaves on the
communications link that support broadcast messages will process the message. As the data transfer
is one way only, broadcast messages are restricted to coil and holding register writes only. A broadcast
sequence can consist of any number of messages, each of which may be individually enabled or
disabled from the application. Each broadcast message counts towards the maximum number of
slave messages allowed for the communication interface.
Note: When using broadcast messages, at least one non-broadcast message addressed to a specific
slave must be configured.
Broadcast mode can be individually enabled for any master device. Select ‘Use Broadcast Mode’ to
enable broadcast messages.
If message control is required (see the modes of operation below), select ‘Use Control Variable’ and
enter the Modbus address of an application variable that will be used to control the message. Where a
control register is defined for either a broadcast or slave message, the message is enabled when the
register contains a zero value. All other values will result in the message being disabled. The data type
used for control variable can be either boolean or integer but not real.
Variable Data Type Value Message
Boolean
False Enabled
True Disabled
Integer
0 Enabled
Non-zero Disabled
Table 6 Modbus Message Control Values