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A Appendices
Symptom: Cannot Communicate or a Communications Error Occurs
The communications wiring is not correct.
The communications line has become
disconnected.
The communications cable is broken.
The communications cable is too long.
The wrong communications cable has
been used.
More than the specified number of
communications devices are connected to
the same communications path.
An end node has not been set at each end
of the communications line.
The specified power supply voltage is not
being supplied to the Digital 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
Digital Controllers, 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 Digital Controller.
The same unit number as the Digital
Controller is being used for another node
on the same communications line.
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 Digital
Controller.
The host device is detecting the absence
of a response as an error after
broadcasting a command.
The host device sent another command
before receiving a response from the
Digital Controller.
The host device sent the next command
too soon after receiving a response from
the Digital Controller.
The communications line became
unstable when Digital Controller power
was turned ON or interrupted, and the
host device read the unstable status as
data.
The communications data was corrupted
from noise from the environment.
*
Refer to the E5
A - 22
Meaning
Correct the wiring.
Connect the communications line securely and tighten the screws.
Replace the cable.
The total cable length for RS-485 is 500 m max.
Use shielded twisted-pair cable for the communications cable. For
detailed wire specifications, refer to 2-2-5 Precautions when Wiring.
When 1:N communications are used, a maximum of 32 nodes may be
connected, including the host node.
Set or connect terminating resistance at each end of the line. If the E5@D
is the end node, 120-Ω (1/2-W) terminating resistance is used. Be sure
that the combined resistance with the host device is 54 Ω minimum.
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
sample program.
Shorten the send data wait time in the Digital Controller or increase the
response wait time in the host device.
The Digital 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.
Initialize the reception buffer in the host device before sending the first
command and after turning OFF the power to the Digital Con
troller.
Try using a slower baud rate.
Separate the communications cable from the source of noise.
Use a shielded, twisted-pair cable for the communications cable.
Use as short a communications cable as possible, and do not lay or loop
extra cable.
To prevent inductive noise, do not run the communications cable parallel
to a power line.
If noise countermeasures are difficult to implement, use an Optical
Interface.
@
D Digital Controllers Communications Manual (Cat. No. H225) for details on errors.
Countermeasures
E5@D Digital Temperature Controllers User's Manual (H224)
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