Modbus Tcp Channel Commands - GE PACSystems RXi User Manual

Chapter 8. Gigabit Ethernet (GbE) Interface Overview and Operation
8.7.2

Modbus TCP Channel Commands

The RXi Ethernet interface supports the following channel commands:
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Note that Modbus TCP channel COMMREQs do not contain a parameter to configure a
timeout value. Enforcing a timeout for a Modbus channel command is at the discretion of the
user and must be implemented in the user application.
Open a Modbus TCP Client Connection (3000)
The Ethernet interface transfers data to or from another Modbus TCP device using a channel.
Up to 16 channels are available for Modbus TCP client communications.
The Open Modbus TCP COMMREQ requests the communication subsystem to associate a
channel with a remote Modbus TCP device. Using the other COMMREQs defined in this
section, the RXi controller can transfer data to and from a remote device.
Once a channel is allocated for Modbus TCP Client communications, the channel remains
allocated (i.e. another protocol cannot use the channel). The channel connection is released
only when:
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The IP address of the remote Modbus TCP device is specified in the Open Modbus TCP
COMMREQ using the standard dotted-decimal format. No other IP address format is
accepted.
The COMMREQ Status Word (CRS) indicates the success or failure of the Open Modbus
TCP Client Connection COMMREQ. If the COMMREQ requests an invalid channel number
or an already allocated channel the COMMREQ fails and the CRS is set to a non-zero value
to identify the failure. Refer to Status Data on page 152 for detailed CRS failure codes.
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Open a Modbus TCP Connection (3000)
Close a Modbus TCP Connection (3001)
Read Data from a Modbus Server Device to the controller (3003)
Write Data from the controller to a Modbus Server Device (3004)
Read/Write Multiple Registers between controller memory and a Modbus Server Device
(3005)
Mask Write Register Request to a Modbus Server Device (3009)
the application program closes the channel
the channel is automatically closed when the controller transitions to STOP,
the Ethernet interface is reset or the underlying TCP connection is terminated
PACSystems* RXi Distributed IO Controller User Manual GFK-2816F