GE P485 - Manual (Page 38)

5–2 P485 MODBUS TO PROFIBUS CONVERTER – USER GUIDE
COMMUNICATION MODEL
The P485 uses pre-configured Modbus RTU commands, acting as a Modbus RTU master.
With Modbus RTU, each transaction is substituted with a pre-defined command that can
be selected from a list of available commands.
It is still possible, though, to define custom message frames by creating a transaction
instead of selecting a pre-defined command. A command is actually a transaction that has
been defined in advance and stored in a list.
SCAN LIST Once the configuration has been downloaded to the P485, the P485 firmware searches the
scan-list, using the defined transactions for communication with the slave-devices.
Each node in the scan-list represents a slave device on the Modbus network. In EnerVista
P485/D485 Setup, each node is given a specific name and assigned an address in standard
Modbus RTU commands. The address must match the internal setting on the slave device.
Figure 5-2: P485 scan list
Basic settings
PARAMETER WINDOW Select ‘Modbus Network’ in the Navigation window to gain access to basic settings in the
Parameter window.
Figure 5-3: Parameter window
COMMUNICATION Refer to Serial interface settings on page 4–13 for details.
MESSAGE DELIMITER The message delimiter value is the minimum time in steps of 10 ms separating the
messages. According to the Modbus specification, the message delimiter has a default
setting of 3.5 characters.If this value is set to “0”, the P485 will use the Modbus standard 3.5
character message delimiter. The time in milliseconds is then dependent on the selected
baud rate, but this is all handled by the P485.
Due to its impact on subnet functionality, use caution when changing this parameter.
NOTE