Inferring Causes From Conditions: Communications Problems; Cannot Communicate Or No Response - Omron E5AR-T User Manual

Section 10 Troubleshooting
10.6 Inferring Causes from Conditions:
Communications Problems

■ Cannot Communicate or No Response

The baud rate differs from the host system.
The communications settings are different from the
host system.
The number of parallel connections exceeds the
specifications.
The length of the transmission path exceeds the
specifications.
Another Controller has the same unit number.
Noise is corrupting the communications data.
Incorrect use of communications devices:
• Optical interface
• RS-232C/RS-485 converter
Incorrect installation of RS-485 terminators.
Communications begin as soon as the power of the
E5AR-T/ER-T is turned ON.
Unstable signals that occur when the E5AR-T/ER-T
is turned ON or OFF are read as host system data.
The host system sends a command before
receiving a response from the E5AR-T/ER-T.
The interval between receiving a response and
sending the next command from the host system is
too short.
Mistake in host system program.
The unit number setting is different from the unit
number specified in the command.
10-10
Possible causes Solution
Make sure that the baud rates are the same.
Make sure that the communications settings are
the same.
Do not exceed the specifications.
• For RS-485, a maximum of 31 nodes can be
connected.
Do not exceed the specifications.
• For RS-485, the total maximum length is 500 m.
Make sure each unit number is set only once.
• Separate the communications cable from the
noise source.
• Use shielded communications cables.
• Use an optical interface.
• Have the program resend the command when a
problem is detected in the response.
Check application methods in the instructions for
each device.
Install terminators only on the devices on the ends
of the transmission path.
Wait at least 2 seconds before beginning
communications after the power is turned ON.
Initialize the host system reception buffer at the
following times:
• Before sending the first command.
• After the power of the E5AR-T/ER-T is turned
OFF.
Make sure that the program always reads the
response after sending a command.
Allow an interval of at least 5 ms after receiving a
response before sending the next command.
• Correct the program.
• Check the command in a line monitor.
• Try executing a sample program.
Make sure the unit numbers match.