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10 TROUBLESHOOTING
MELSEC-Q
10 TROUBLESHOOTING
This chapter explains the definitions of errors that may occur during data communication between the Q series C24 and external devices, and the corrective actions.
10.1 Checking the Status of the Serial Communication Module
10.1.1 Checking the LED ON status, communications error status, and switch setting status of the serial communication module
This section explains how to check the status of communication between the Q series
C24 and external devices, the transmission status of the Q series C24, and the switch setting status of the Q series C24.
When a communication problem occurs, check the error status using one of the following procedures:
(1) Checking the module status and error codes in the detailed module information screen of the GX Developer diagnostic functions
[Startup procedure]
GX Developer [Diagnostics] [System monitor]
Module's Detailed Information
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[Displays]
• Module
The following information is displayed:
Module name : The name of the module installed
I/O Address : The start input/output signal (number) of the target module
Implementation Position: The slot position where the module is mounted
Product information : Product information
The last character of the product information indicates the function version of the module.
(Example) If the last character is "B," it means that the module is of function version B.
• Unit access (Module access)
Displays access permissions when the Ready signal (X1E) is turned on and the WDT error signal (X1F) is turned off.
• Status of I/O Address Verify
Displays whether or not the module for which the user set the parameters matches the module installed.
• Remote password setting status
Displays the setting status of the remote password.
• Present Error
Displays the error code of the latest error occurrence.
• Error Display
Displays the error codes for any errors that have occurred in any of the functions being used.
• Error details, corrective action
Displays the error details and corrective action for the error code selected in
Error Display.
(2) Checking using the hardware information screen of the GX
Developer diagnostic functions
[Startup procedure]
GX Developer [Diagnostics] [System monitor]
Module's Detailed Information H/W Information
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[Displays]
1) H/W LED Information Right side (Left side: CH1 information/
Right side: CH2 information)
Displays the transmission status and the communications error status of the Q series C24.
(Displays 201
H
/202
H
of the buffer memory.)
Buffer memory address 201
H b15 to
For system
1: Lit/Communication error
0: not lit/No communication error b8 b7 b6 b5 b4 b3 b2 b1 b0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 (Information of CH1 side)
SD WAIT
SIO
PRO.
P/S
C/N
NAK
ACK.
NEU.
b15 b14 b13
Buffer memory address 202
H
1/0 1/0 to b8 b7 b6 b5 b4 b3 b2 b1 b0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 (Information of CH2 side)
For system
SD WAIT
SIO
PRO.
P/S
C/N
NAK
ACK.
NEU.
CH2 ERR.
CH1 ERR.
2) H/W SW Information Parameter
The switch information of the Q series C24 is displayed.
Numbers 1 through 5 correspond to switches 1 through 5 shown in
Section 4.5.2.
(See Section 4.5.2 of the User's Manual (Basic).)
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(3) Checking by GX Configurator-SC
Display the "Monitor/test others" screen.
For details on display screens, see Section 8.6.9 of the User's Manual (Basic).
No.
Status signal name
(4) Description of LED ON status and communications error status
Description
Description when ON
(when LED is turned on (when LED is turned off
(1))
Description when OFF
(0))
Initial state
MC
Related protocol
Non procedure protocol
Bidirectional protocol
1 SD WAIT Transmission wait status
Waiting for data transmission
2 SIO SIO error status
Overrun or framing error occurred.
OS area is full.
Received data was deleted.
3
4
5
PRO.
P/S
C/N
Communication protocol error status
Status of parity error or sum check error
Access status with the
PLC CPU
(
Error occurred.
Error occurred.
1
)
6
7
8
9 CH2. ERR
10
NAK
ACK.
NEU.
CH1. ERR
Abnormal completion status
Normal completion status
Neutral status
Waiting to receive command
Error occurrence status on CH2 side
Error occurrence status on CH1 side
Abnormal completion transmission
Normal completion transmission
Neutral
Switch setting error
Mode switching error
Transmission error
Reception error
On-demand error
Data transmission start OFF
Normal
Normal
Normal
Normal
Normal completion transmission
Abnormal completion transmission
Command reception
Normal
(
OFF
OFF
OFF
OFF
OFF
OFF
OFF
2
OFF
OFF
)
—
—
—
1 C/N turns on in the following cases:
• An external device issued a data read request to the PLC CPU when write during RUN is set to prohibit in the switch settings by GX Developer (see
Section 4.5.2).
For functions that cannot be used when write during RUN is set to prohibit, see the explanation section in each command list of the Reference Manual.
• When an error has occurred during access between the Q series C24 and the
PLC CPU.
2 NEU. is valid when a target interface is set to use the MC protocol.
When the target interface is set to other than the MC protocol, the status of NEU.
is off.
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(a) When a communication error occurs, take corrective action according to
Section 10.3.
(b) The initial status of the LED ON and communications error indicates the status when the Q series C24 starts up by turning on the power or resetting the PLC CPU.
(c) Each of the communications error status, C/N to SIO, CH1 ERR. and CH2
ERR., turns on when an error occurs, and keeps its on-status even after the communication returns to normal.
The PLC CPU can check the aforementioned LED ON status and communications error status, and initialize any error information using read/write to the buffer memory of the Q series C24 and input/output signals.
Initialize the error information according to Section 10.1.2.
(d) NAK to NEU. (No. 6 to 8) turn on/off depending on the status.
(e) SD WAIT turns on when data cannot be sent to the external device by the transmission control of the Q series C24 (waiting for data transmission).
• When transmission cannot be started.
• When a transmission pause request is received during data transmission.
(DSR signal is off, reception by DC3)
SD WAIT turns off when transmission becomes possible and data transmission is started/resumed.
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10.1.2 Initializing error information of the serial communication module
This section explains the ERR. LED ON factors and the error code initialization (clear) for the Q series C24.
(1) ERR. LED ON factors
When any of the following errors occurs, its error code is stored in the buffer memory corresponding to the interface (CH) where the error occurred, and the
ERR. LED turns on.
Cause of error
Address
Error code storage buffer memory
Name
CH1 CH2
MC
Applicable protocol
Nonprocedure protocol
Bidirectional protocol
Switch setting error
Mode switching error
On-demand execution error
Data transmission error
Data reception error
MC protocol transmission error
Monitoring device error
256
H
257
H
258
H
203
H
Switch setting error, mode switching error storage area
266
H
On-demand execution result storage area
267
H
Data transmission result storage area
268
H
Data reception result storage area
025A
H
026A
H
MC protocol transmission error code
2205
H
2305
H
PLC CPU monitoring function execution result
(2) Turning off the ERR. LED and initializing the error codes by GX
Configurator-SC (Refer to Section 8.6.10)
(a) When turning off the ERR. LED and initializing the error codes
By making the CH ERR. clear request on the "Monitor/Test" screen, the
ERR. LED of the Q series C24 turns off and the stored error codes are initialized.
(b) When initializing the communication error information
By making the Communication error clear request for CH and to turn LED off on the "Monitor/test others" screen, the LEDs (ERR., NEU.) of the Q series C24 turn off and the communication error information is initialized.
(3) Turning off the ERR. LED and initializing the error codes by sequence program
(a) Input signals used to notify of error occurrences and output signals used to initialize the error code
I/O signal
Input signal
Output signal
Name of status information Description/function
XE Error occurrence on CH1 side
XF Error occurrence on CH2 side
Turns on upon error occurrence in CH1 interface.
Turns on upon error occurrence in CH2 interface.
YE CH1 Error information initialization request Turns on when initializing error code of interface on CH1 side.
YF CH2 Error information initialization request Turns on when initializing error code of interface on CH2 side.
Initialization of error code is continuously performed when output signal (YE/YF) is on.
POINT
The CHn side error information can be initialized by an off request to the LED off request area (address 1
H
) of the buffer memory. By using output signals YE to YF, the error codes stored in the above buffer memory can further be initialized
(cleared).
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(b) Initializing communication error information by writing
Communication error information can be initialized by writing "1" to the corresponding bit in the buffer memory addresses 0
H
to 1
H
.
The displayed LEDs and communication error information may be turned on/off in the following cases:
• NEU. to NAK turn on/off depending on the status.
• C/N to SIO turn on when errors occur and keep the ON-status even after the operation returns to normal.
1) LED and communications error information initialization request area
(address: 0
H
to 1
H
)
The contents of the error information corresponding to each bit in this request area are the same as those for the LED ON/communication error status storage area (address: 201
H
to 202
H
).
For more details, see Section 10.1.1 (1).
The following describes the correspondence between the LED OFF request areas and the LED ON status storage areas:
• Communication error clear request area for CH1 and to turn LED off
(address: 0
H
) LED ON status and communication error status area on CH1 side (address: 201
H
)
• Communication error clear request area for CH2 and to turn LED off
(address: 1
H
) LED ON status and communication error status area on CH2 side (address: 202
H
)
2) Example of a program for turning off displayed LEDs
The following shows an example of a program that issues an initialization request for all the communication error information of CH1 and CH2.
(Input/output signals X/Y00 to X/Y1F of QC24)
Example of TO instruction
Turn off command
Writes 00FF
H
to address 0
H
and C0FF
H to address 1
H
.
POINT
(1) Initialization requests are valid only when write operation is performed.
The initialization requests clear all data in the LED ON and communication error information storage area (201
H
to 202
H
) at the same time.
Furthermore, when initialization of error information on the CH1 and CH2 sides is requested, XE and XF also turn off.
(2) Data written to the buffer memory address 0
H
to 1
H
is cleared after initialization processing.
(3) If errors persist even after completion of the initialization processing, the corresponding communication error information is stored again and the corresponding bit in the LED ON and communications error status storage area (201
H
to 202
H
) turns on (1).
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Turn off/clear command
Turn off/clear command
Read command
MELSEC-Q
(c) Examples of programs that initialize displayed LED and communication error information
The following shows examples of a program that reads error codes when errors described in (1) above occur in an interface on the CH1 side and initializes the displayed LED and communication error information.
Incorporate the necessary part of the program.
(Input/output signals X/Y00 to X/Y1F of the Q series C24)
1) When data is communicated using the MC protocol
Reads LED and communication error information from address 201
H
.
Reads switch setting error description from address 203
H
.
Reads data transmission/reception results from address 256
H
to 258
H
.
Requests initialization of error information on the
CH1 side and clearing of error codes in the buffer memory.
Requests initialization of error information on the CH1 side and clearing of error codes in the buffer memory.
Check the error codes and take corrective action according to Section 10.2.
2) When data is communicated using the non procedure or bidirectional protocol
Reads LED and communication error information from address 201
H
.
Reads switch setting error description from address 203
H
.
Reads data transmission/reception results from address
257
H
to 258
H
.
Writes initialization request such as for displayed LED to address 0
H
.
Requests initialization of error information on the CH1 side and clearing of error codes in the buffer memory.
Check the error codes and take corrective action according to Section 10.2.
REMARK
When data is communicated using the MC protocol, the displayed ERR. LED may not be turned on if the Q series C24 sends an NAK message to the external device in response to the command message.
Error codes (see Section 10.2) corresponding to the error content when the NAK message is sent back to the external device are stored in the following areas. (when communicating with an A compatible 1C frame, the error codes differ from the transmission error code.)
When checking error codes transmitted by the PLC CPU, incorporate the following program (in case of the interface on the CH1 side).
Reads transmission error codes from address 25A
H
.
Clears error codes.
Check the error codes and take corrective action according to Section 10.2.
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10.1.3 Reading the RS-232 control signal status
This section explains how to read the control signal status stored in the buffer memory during communication using RS-232 interface.
When GX Configurator-SC is used, check the status using the "Transmission control and others monitor/test" screen (see Section 8.6.3).
When a transmission problem occurs, read operation is executed to check the signal on/off status of the RS-232 interface.
(1) RS-232 control signal status storage area (address: 254
H
, 264
H
)
The status of the RS-232 signals is stored in buffer memory addresses 254
H
and
264
H
as follows:
Buffer memory address
254
H b15
264
H to
0
0 b6 b5
1/0 b4 b3
1/0 1/0 b2
1/0 b1
1/0 b0
1/0
(Information on CH1 side)
1/0 1/0 1/0 1/0 1/0 1/0
(Information on CH2 side)
1 : ON
0 : OFF
System area for QJ71C24 (-R2)
RS
DSR
DTR
CD
CS
RI
Read command
REMARK
(1) For more details on signals for RS-232, see Section 3.2.1.
(2) Signals output from the Q series C24 side (RTS and DTR) are controlled by the operating system (OS) of the Q series C24.
They cannot be directly controlled by the sequence program.
(3) There is a maximum delay of 100 ms in signal status stored in the buffer memory above.
(2) Example of a program that reads from RS-232 control signal status storage area
The following shows an example of a program that reads the RS-232 control signal status.
(input/output signals X/Y00 to X/Y1F of the Q series C24)
Example of FROM instruction
Reads the status of RS-232 control signal on the CH1 side from address 254
H
.
Reads the status of RS-232 control signal on the CH2 side from address 264
H
.
D0
D1 b15 to b6 b5
0 b4 b3 b2 b1 b0
0 0 1 1 1
0 0 1 1 1 0
DTR signal: ON, DSR signal: ON, RTS signal: ON
CD signal: ON, DTR signal: ON, DSR signal: ON
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10.1.4 Reading the data communication status (Transmission sequence status)
This section explains how to read the current status of the data communication using the MC protocol stored in the buffer memory.
When GX Configurator-SC is used, check the status using the "MC protocol monitor" screen (see Section 8.6.4).
When a transmission problem occurs, read operation is executed to check the status of the data communication using the MC protocol.
(1) Transmission sequence status storage area (address: 255
H
and 265
H
)
The status of data communication using the MC protocol is stored as a numerical value in buffer memory addresses 255
H
and 265
H
.
Buffer memory address
255
H b15 to
0 to 9 b0
(Information on the CH1 side)
265
H
0 to 9
(Information on the CH2 side)
The following shows the correspondence between the numerical values in the transmission sequence status storage area and the data communication status.
External device
Request from an external device
E
N
Q
Message wait
ACK or
NAK
Q series C24
Request to CPU
Response from
CPU
"6" "1"..."6" is repeated afterward.
Stored value
0 1
2
3 4 5 6
Values 7 to 9 are stored when "mode switching" or "initialization
of transmission sequence" is performed.
REMARK
When the target interface is not set to use the MC protocol, "0" is stored in the transmission sequence status storage area.
(2) Example of a program that reads from transmission sequence status storage area
The following shows an example of a program that reads from the transmission sequence status storage area.
(input/output signals X/Y00 to X/Y1F of the Q series C24)
Example of FROM instruction
Read command
Reads the status of data communication on the CH1 side from address 255
H
.
Reads the status of data communication on the CH2 side from address 265
H
.
D0
D1 b15 to
0
4 b0
The CH1 side is waiting to receive a command message, and is using non procedure or bidirectional protocol.
CH2 is accessing the PLC CPU upon reception of a command message.
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10.1.5 Reading the switch setting status
This section explains how to read the switch setting status of the Q series C24.
When GX Configurator-SC is used, check the status in the "Monitor/test others" screen
(see Section 8.6.9).
REMARK
(1) The switch settings can be changed when the mode is switched or when the
UINI instruction is executed. (The station No. setting can be changed only when the UINI instruction is executed.)
For the mode switching, refer to Chapter 15 of the User's Manual (Application).
For the UINI instruction, refer to Chapter 17 of the User's Manual (Application).
(2) For the switch settings, refer to Section 4.5.
(1) Setting status storage area
The switch settings by GX Developer and setting error information are stored in different areas of the buffer memory shown below.
Buffer memory address 200
H b15
1) Station number storage area (address: 200
H
) to
0 to 31 b0
(Station number)
Buffer memory address 203
H
2) Switch setting error/mode switching error storage area (address: 203
H
) b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
Ignore (including b2 and b6)
Station number of the Q series
C24 is outside the range.
Linked operation setting error
(see Section 4.5.2 (2)).
CH2 CH2 CH2 CH1
(1: Error, 0: Normal)
CH1 CH1
Communication protocol number on CH side is outside the range.
Communication rate on CH side is outside the range.
Mode switching request was issued when the setting modification allow/prohibit was set to prohibit.
3) Communication protocol storage area (address: 250
H
and 260
H
) b15 to b0
Buffer memory address 250
H
0 to 8 (Information on the CH1 side)
260
H
0 to 7
(Information on the CH2 side)
4) Transmission setting status storage area (address: 251
H
and 261
H
)
Buffer memory address 251
H b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
(Information on the CH1 side)
261
H
0 0 0 0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 (Information on the CH2 side)
Communication rate setting
Setting modification allow/prohibit
Operation setting
Data bit setting
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(2) Example of a program that reads from the setting status storage area
The following shows an example of a program that reads the setting of various switches of the Q series C24 from the setting status storage area.
For details on XE and XF of the input/output signals used in the program, see
Section 10.1.2 (3).
(input/output signals X/Y00 to X/Y1F of the Q series C24)
Example of FROM instruction
Reads error description from address 203
H.
Reads station number setting and switch setting description from address 200
H
.
Reads communication protocol setting and transmission setting description on the CH1 side from addresses 250
H
to 251
H
.
Reads communication protocol setting and transmission setting description on CH2 from addresses 260
H
to 261
H
.
Restarts the Q series C24 after checking the error code and resetting switches.
D0 b15b14b13b12 b11b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
Error description (1: Communication protocol number setting error)
D1
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
D2
0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 1
D3
0 0 0 0 0 1 0 1 0 0 0 0 1 0 1 0
D4
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
D5
0 0 0 0 0 1 0 1 0 1 1 0 1 0 1 0
Setting station number of the Q series C24 (0).
CH1 side
CH2 side
Communication protocol setting number (9).
(transmission setting description)
Communication protocol setting number (1).
(transmission setting description)
Displays communication protocol number setting error status on the CH1 side
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10.1.6 How to read the current operation status
This section explains how to read the current operation status of the Q series C24.
When GX Configurator-SC is used, check the status in the "Transmission control and others monitor/test" screen (see Section 8.6.3).
REMARK
• The status of the switch settings by GX Developer can be checked by performing read operations as described in Section 10.1.5.
• Refer to Section 4.5 for the switch settings.
(1) Operation mode status storage area
The current operation status of the Q series C24 is stored into the following buffer memory areas.
1) Station No. storage area (address: 24F
H
)
Buffer memory address 24F
H b15 to
0 to 31 b0
(Station No.)
Buffer memory address 252
H b15
2) Communication protocol status storage area (addresses: 252
H
and 262
H
) to
1 to 7 b0
(Information on the CH1 side)
262
H
1 to 7 (Information on the CH2 side)
Mode number currently operating
3) Transmission status storage area (address : 253
H
, 263
H
)
Buffer memory address 253
H b15 b14 b13 b12 b11 b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
(Information on the CH1 side)
263
H
0 0 0 0
1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0 1/0
(Information on the CH2 side)
Communication rate setting Operation setting
Data bit setting
Parity bit setting
Even/odd parity setting
Stop bit setting
Sum check code setting
Write during RUN setting
Setting modification allow/prohibit
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(2) Example of a program that reads from the current setting status storage area
The following shows an example of a program that reads from the switch setting status storage area for current operation of the Q series C24.
For details regarding XE and XF of the input/output signals used in the program, see Section 10.1.2 (3).
(input/output signals X/Y00 to X/Y1F of the Q series C24)
Example of FROM instruction
Reads error description from address 203
H
.
Reads CH1 side communication protocol status and transmission status from addresses 252
H
to 253
H
.
Reads CH2 side communication protocol status and transmission status from addresses 262
H
to 263
H
.
Reads station No. from address 24F
H
.
After checking error codes and changed setting values, designate the correct setting values and switch mode.
D0 b15b14b13b12 b11b10 b9 b8 b7 b6 b5 b4 b3 b2 b1 b0
0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0
Communication protocol
D1
0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0
Error description (2: Communication rate error)
CH1 side
Setting communication protocol number 6
(transmission setting description)
D2
0 0 0 0 1 1 1 1 0 0 0 0 1 0 1 0
D3
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1
D4
D5
0 0 0 0 0 1 0 1 0 1 1 0 1 0 1 0
CH2 side Setting communication protocol number 1
(transmission setting description)
0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 Station No. 1 being set.
While the CH1 side is set to the non procedure protocol and the CH2 side is set to the MC protocol (format 1), this indicates the communication rate setting error on the CH1 side.
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