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9.4 Troubleshooting in bus connection
9.4.1 Locating error positions
(2) Error messages appearing due to faulty ACPU bus connection and measure against errors
Error
Code
Error
Messages
Check Timing
Cause and check point
Error detail Remedy
Correspond-
ing CPU
22 WDT ERR.
When an End
instruction is exe-
cuted
(1) The scanning time exceeds
the calculation congestion
monitoring time.
(2) The scanning time may be
extended by waiting for a
response from an SP
module that is down, and
errors may occur
simultaneously.
(1) Use the error history to check whether
simultaneous occurrence errors are
present.
(2) Refer to the SP module down check
points.
ACPU
31
UNIT VER-
IFY ERR.
When an End
instruction is exe-
cuted
The information stored in the cards
of the module installed in the base
module and the communication
module of the GOT is different
from that read at the initial time.
(If an error occurs on a module
(vacant) other than that installed in
the base module, the mis-opera-
tion may be caused by noise.)
Check the faulty module at special resisters
D9116 to D9123.
(1) Check that the module and the cables
are connected correctly.
(2) Check that the PLC and the GOT are
earthed correctly.
40
CONTROL
_BUS
ERR.
During execution of
FROM/TO instruc-
tion set
When the FROM/TO instruction is
executed, an imprecise response
is returned from the special func-
tion module (including the GOT).
Check the faulty module from the error step.
(1) Check that the module and the cables
are connected correctly.
(2) Replace the faulty module with a new
one.
(3) Check that the PLC and the GOT are
earthed correctly.
At CPU power ON/
At reset
At the time of initial communica-
tion, an imprecise response is
returned from the special function
module (including the GOT).
(1) Check that the module and the cables
are connected correctly.
(2) Because a faulty module cannot be
located, remove the modules one by
one until no CONTROL_BUS ERR.
message appears to indicate the
module where the error occurs.
(Because the modules are removed, SP.
UNIT ERR. message may appear. Stop
transmitting the FROM/TO instruction to
the applicable module.)
41
SP. UNIT
DOWN
During execution of
FROM/TO instruc-
tion set
The special function module was
accessed during the execution of a
FROM/TO instruction set, but
there was no response.
Check the faulty module from the error step.
(1) Check that the module and the cables
are connected correctly.
(2) Replace the faulty module with a new
one.
(3) Check that the PLC and the GOT are
earthed correctly.
At CPU power ON/
At reset
At the time of initial communica-
tion, a response is not returned
from the special function module
(including the GOT).
(1) Check that the module and the cables
are connected correctly.
(2) Replace the faulty module with a new
one.
(3) Check that the PLC and the GOT are
earthed correctly.
43
I/O INT
ERR.
During interrupt
An imprecise interrupt occurs to
the PLC CPU.
44
SP. UNIT
LAY ERR.
At CPU power ON/
At reset
Too many modules are installed
(see the PLC CPU specification).
(1) Check the number of installed modules.
(2) Check the number of extension stages
and the I/O slot numbers.
46
SP. UNIT
ERR.
During execution of
FROM/TO instruc-
tion set
The FROM/TO instruction is exe-
cuted to any module other than the
special function module.
(1) Review the sequence program.
(2) Check the number of extension stages
and the I/O slot numbers.