MODBUS
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RS485/RS232 Communications Interface
Configuring the PLC/SCADA Supervisor
By referring to the Parameter Specification Table in the 650 or 650V Software Product Manual,
you can enter the parameter information you require.
It provides the information in the following way:
Type
The first page of the Parameter Specification Table chapter details parameter types.
The Type column indicates each parameter's type.
TAG
The TAG column provides the unique identification tag number.
Example only
MODBUS RTU Communications
A MODBUS RTU communication network can have only one Master, and one or more Slave
devices.
•
Each Slave has a unique “device address”
•
The device address “0” is a special case and is used for messages that are broadcast to all
Slaves. This is restricted to parameter write operations.
•
The unit supports a subset of MODBUS RTU function codes.
•
The data includes parameters referenced by a “parameter address”.
•
Sending a communication with a unique device address causes only the device with that
address to respond. That device will check for errors, perform the requested task and then
reply with its own address, data and check sum.
•
Sending a communication with the device address “0” is a broadcast communication that
sends information to all devices on the network. Each device performs the required action
but does not transmit a reply.
How is the Information Transferred?
A typical transaction consists of a request sent from the Master followed by a response from the
Slave.
A message consists of a sequence of characters which we identify as:
•
Device Address
•
Function Code
•
Data
•
Error Check Data
•
End of Transmission
Device Address
Each Slave has a unique 8-bit device address. The Gould MODBUS Protocol defines the
address range limits as 1 to 247 (device address 0 is the broadcast message to all slaves
simultaneously).
Summary of Contents for 6513
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