Check Of Identical Slave - Master Configuration; Check The Cabling Of The Rs485; Check The Transmit - Receive Indicators; Check The Function Called And The Register Addresses - Hitachi Abb Rvt Installation Und Betriebsanleitung

7.2. Check of identical Slave – Master configuration
In any case the master must have the same communication parameters as the controller:
Enter the MODBUS menu under:
COMMUNICATION - I/O CONFIGURATION – COM. SETTINGS – MODBUS
– Choose a slave address
– Select the right communication speed (baud rate)
– Select the right parity checking
– Select the right number of stop bits

7.3. Check the cabling of the RS485

– The non-inverting and the inverting output wires should be cabled respectively on non-inverting and inverting input
respectively. No communication will take place if non-inverting wires are mixed with inverting wires.
– Load termination resistors are important at both end of the network to avoid distortion due to reflections in the
communication line. Check that the 'Load switch' is at the right position (ON or OFF) according to the network con-
figuration.
– Connection of a ground wire and presence of a shielding will improve reliability.
7.4. Check the Transmit – Receive indicators
This is a convenient way to check the presence of TX – RX signals:
– The Receive Led (yellow Led) indicates that a Modbus query is being received by the RS485 Modbus adapter.
– The Transmit Led (green Led) indicates that a Modbus response is being transmitted from the RS485 Modbus
adapter.
If the Rx Led and the Tx Led never lit, the problem may come from:
– The wires of the RS485 cable are not properly fixed or cabled
– The query is not sent (see the application software)
– The controller and then the RS485 are not powered
If only the Tx Led never lit, the problem may come from:
– The controller settings are not correct (check communication parameters settings)
– The controller entered the 'listen only' mode (reset the controller or send the required command to disable the 'lis-
ten only' mode.)
• The master sends Broadcast messages (address 0) which are to be acted on by all connected devices and do
not require a reply

7.5. Check the function called and the register addresses

To ensure that a read or write message to a Modbus address will produce a normal response, check that the register
address corresponds exactly to the desired data requested.
In Modbus register addressing there are several categories of register, including holding registers (numbered from
40001 upwards) and input registers (numbered from 30001 upwards). The category of register addressed is implicit in
the Modbus function used, e.g. function 03 addresses holding registers and function 04 addresses input registers.
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DOCUMENT ID
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