Communications Errors - Omron E5ZN Operation Manual

Communications Errors

8-2

Communications Errors

Communications Not Possible or No Response
Communications Baud rate of the E5ZN is different from that of the
conditions host.
Communications method of the E5ZN is different
from that of the host.
Connections Excessive number of E5ZN Units are connected
in parallel.
Transmission path is too long.
Same unit number has been allocated more than
once on the same transmission path.
Communications data error due to ambient noise. • Move the communications cable away from the
Mistake in the use of the Optical Interface and
RS-232C/RS-485 Converter Units.
Terminators incorrectly attached to RS-485.
Program System begins communications without any inter-
val after the E5ZN Units are turned ON.
Unstable signal of the E5ZN, which is generated
when the E5ZN is turned ON or OFF, is read as
data by the host.
Host sends commands to the E5ZN before receiv-
ing any response from the E5ZN.
Interval between the time the host receives a
response and sends a command is too short.
Program of the host is incorrect.
Settings Unit numbers set with the selectors are different
from those set using the commands of the host.
Probable cause Remedy
Set the same rate.
Match the communications method of the E5ZN
to the host's communications conditions.
Do not connect an excessive number of E5ZN
Units.
• The number of E5ZN Units that can be con-
nected to the host for RS-485 communications
is 16 max.
The transmission path must be within the permis-
sible range.
• The maximum RS-485 transmission path is
500 m in total.
Make sure that different numbers are assigned to
all the E5ZNUnits that communicate with the host.
source of noise.
• Use shielded communication cables.
• Use an Optical Interface.
• Write a program that makes it possible for the
host to detect a response error for any com-
mand that the host transmits and to re-transmit
it again.
Refer to the datasheets of the Optical Interface
and RS-232C/RS-485 Converter Units used.
Attach terminators only to the devices at each end
of the communications path.
Write a program so that the system starts com-
munications with an interval of 4 s min. after the
E5ZN Units are turned ON.
Initialize the reception buffer of the host at the fol-
lowing stages.
• Before the host transmits the first command.
• After the E5ZN is turned OFF.
Write a program enabling the host to read the
response after the host sends any command.
The interval between the time the host receives a
response and sends a command must be 5 min-
utes minimum.
• Correct the program.
• Check the command with the line monitoring
function.
• Run a sample program with the host.
The unit numbers must coincide.
Section 8-2
149