Omron E5CN User Manual page 289

Symptom: Cannot Communicate or a Communications Error
Occurs
Meaning
The communications wiring is not correct.
The communications line has become dis-
connected.
The communications cable is broken.
The communications cable is too long.
The wrong communications cable has been
used.
More than the specified number of communi-
cations devices are connected to the same
communications path for RS-485 communi-
cations.
An end node has not been set at each end of
the communications line for RS-485 commu-
nications.
The specified power supply voltage is not
being supplied to the Controller.
The specified power supply voltage is not
being supplied to an Interface Converter
(such as the K3SC).
The same baud rate and communications
method are not being used by all of the Con-
trollers, host devices, and other devices on
the same communications line.
The unit number specified in the command
frame is different from the unit number set by
the Controller.
The same unit number as the Controller is
being used for another node on the same
communications line for RS-485 communica-
tions.
There is a mistake in programming the host
device.
The host device is detecting the absence of a
response as an error before it receives the
response from the Controller.
The host device is detecting the absence of a
response as an error after broadcasting a
command (except for SYSWAY).
The host device sent another command
before receiving a response from the Control-
ler.
The host device sent the next command too
soon after receiving a response from the
Controller.
264
Correct the wiring.
Connect the communications line securely and tighten the screws.
Replace the cable.
The total cable length is 500 m maximum for RS-485 and 15 m maximum
for RS-232C communications. To extend the communications distance for
RS-232C communications, use OMROM's Z3R Optical Interface.
Use a shielded, twisted-pair AWG24 to AWG14 (cross-sectional area of
2
0.205 to 2.081 mm ) cable for the communications cable.
When 1:N RS-485 communications are used, a maximum of 32 nodes
(including the host node) can be connected.
Set or connect terminating resistance at each end of the line. If the E5CN,
E5AN, or E5EN is the end node, use 120-Ω (1/2-W) terminating resis-
tance. The combined terminating resistance with the host device must be
at least 54 Ω.
Supply the specified power supply voltage.
Supply the specified power supply voltage.
Set the same values for the baud rate, protocol, data length, stop bits, and
parity on all nodes.
Use the same unit number.
Set each unit number for only one node.
Use a line monitor to check the commands. Check operation using a sam-
ple program.
Shorten the send data wait time in the Controller or increase the response
wait time in the host device.
The Controller does not return responses for broadcast commands.
The response must always be read after sending a command (except for
broadcast commands).
After receiving a response, wait at least 2 ms before sending the next
command.
Countermeasures
Appendix