User guide

<6. Modbus communication Troubleshooting>
6-1
IM 01C25R05-01EN
6. Modbus Communication
Troubleshooting
If any abnormality appears in the Modbus communication, use the troubleshooting lists below to isolate and
remedy the problem. Refer to IM01C25R05-01EN “EJX910A and EJX930A Multivariable Transmitters” for the
transmitter troubleshooting. Since some problems have complex causes, these lists may not identify all. If you
have difculty isolating or correcting a problem, contact Yokogawa service personnel.
Abnormality
phenomenon
Remedy
Priority Item Explanation Reference
No response from the
device
1 Device power Conrm if the device power is on. 2.1.2 Wiring
2 Communication
wiring
Conrm if the Modbus communication wiring is correct.
Try switching communication wiring A with B.
2.1.2 Wiring
3 Modbus
communication
setting
Conrm if the Modbus communication setting (Slave
Address, Baud rate, Stop bit, Parity, Data length) is
same as the host and terminator is correctly set in the
RS485 bus.
EJX Multivariable transmitter communication setting
(Slave Address, Baud rate, Stop bit, Parity, Data length)
is conrmed by integral indicator display when powering
on. EJX Multivariable transmitter communication setting
(Baud rate and terminator setting) is conrmed by the
hardware switch.
2.1.1 The Hardware
Switch
2.2 Integral Indicator
Display When
Powering On
4 Host timeout
setting
Conrm if the timeout setting of host is not shorter than
3 seconds.
3.2 Communication
Setup
5 Host
communication
period
Conrm if the host communication period between
receiving the response from the device and sending the
request to the device is set larger than 100 ms under the
multi drop connection.
3.2 Communication
Setup
6 Modbus
specication
Conrm if the host Modbus communication matches to
Modbus specication.
E.g.
• Sending frame conforms Modbus specication.
• Max transmit frame size is not exceeding 200byte.
• CRC value is correct.
5. Modbus
Communication
7 Noise Conrm if the noise is not injected in the signal on
RS485 bus. We recommend isolated RS485 USB
Adaptor for connecting PC to EJX Multivariable
Transmitter.
2.1.2 Wiring
8 Host is not
damaged
Conrm the host or RS-485 USB Adaptor is not
damaged by conrming monitor LED. Do not connect
MODBUS (RS-485) wiring to Power terminals. It may
damage RS-485 adaptor.
2.1.2 Wiring
9 Device is not
damaged
Contact Yokogawa service personnel and conrm the
EJX Multivariable transmitter is not damaged.
Do not connect power wiring to the MODBUS (RS-485)
terminals. It may damage EJX Multivariable Transmitter.
The EJX Multivariable Transmitter power supply is not
electrically isolated from the RS-485 bus.
2.1.2 Wiring
In the case that
Exception code
ILLEGAL FUNCTION
(0x01) is returned
1 Device received unsupported function code.
Conrm if the host Modbus communication matches to
Modbus specication or EJX Multivariable transmitter
Modbus communication specication.
Conrm the host is not sending “Function code 6:
Write Single Register” which is not supported by EJX
Multivariable transmitter.
5. Modbus
Communication
In the case that
Exception code
ILLEGAL DATA
ADDRESS (0x02) is
returned
1 Device is under “write protect” status. Conrm “write
protect” setting.
2.1.1 The Hardware
Switch
3.4.6 Software Write
Protection
2 Device received Read/ Write request on unsupported
address. Conrm host setting.
5. Modbus
Communication
In the case that
Exception code
ILLEGAL DATA VALUE
(0x03) is returned
1 Received data size and quantity value in the frame is not
same. Conrm host setting.
5. Modbus
Communication
2 Received data other than ON (0xFF00) or OFF (0x0000)
for writing Coil. Conrm host setting.
5. Modbus
Communication