User guide

set ia
142 Chapter 2 Command Descriptions
rbx={off|half} (modbusrtu--(slave only))
Enables the serial slave driver to handle Report-By-Exception (XMIT)
writes between polls.
A pilot Report-By-Exception (or XMIT) handler has been added to the
Modbus/RTU serial slave driver. The Digi device pauses between slave
polls to receive potential “Master Requests” initiated by the slave. Just as
with a serial Master-attached configuration, the Modbus/RTU “slave
address” is used with the IA route table to determine the remote
destination.
Behavior is assumed to be half-duplex, and the exact behavior of the
slave device after a collision where both units try to send a request at the
same time is unpredictable. The Digi device will normally ignore the XMIT
request and treat its own request as a timeout.
Using the “rbx:” option and Report-by-Exception writes involves several
requirements:
• The port must be set to “type=slave” and the protocol to
“protocol=modbusrtu.”
• Only one slave may be present on the serial line; multi-drop is not
permitted.
• The “fixedaddress” option must be set to address of the slave. All
other values are assumed to be XMIT transactions.
• XMIT requests MUST NOT use the fixed address of the slave.
• The “lineturndelay” option must be set to at least 50 milliseconds to
provide a window of opportunity for the XMIT function to send a
request.
rmextfunc (modbusrtu, modbusascii, modbustcp)
Used to remove Modbus function codes from the list of those using the
"exttimeout" option instead of the "messagetimeout" option. See the
"exttimeout" option for more details.
rtutimeout (obsolete)
This option is obsolete. Instead, use the “chartimeout” option, described
in "Options for configuring serial port-connected devices" on page 130.
srvecho={on|off} (chat)
Tells the chat protocol engine whether the attached device will echo
messages. If the attached device echoes, then the chat protocol engine
does not forward client messages to other clients. If the attached device
does not echo, the chat protocol engine must forward a copy of client
messages to other clients. The default is "on."
start=”pattern” (custom)
The Digi device uses this character pattern to detect an start of a
message. Refer to the "end" option for the rules and guidelines for
specifying this string. The default is “” or no pattern.