10 TROUBLESHOOTING
10.3.3Troubleshooting when the Q series C24 does not return a response message even though an external device transmitted a message and the "RD" LED blinked
Symptom | Cause |
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| Corrective action | MC |
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| • | Check if the communication protocol is set |
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| correctly. |
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| • Check if the mode was switched without using |
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| • Communication protocol |
| the buffer memory mode switching area. |
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| Note |
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| is set incorrectly. |
| • The communication protocol setting contents |
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| and the communication protocol in the current |
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| operation can be checked at buffer memory |
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| addresses 250H to (CH1) and 260H (CH2). |
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| • When "Check CD | • | Since the message is initialized (skipped reading) |
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| when the CD terminal is turned OFF when "Check |
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| terminal" was set, the CD |
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| CD terminal" is set, change the wiring so that the |
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| terminal was turned OFF. |
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| CD terminal remains on all the time. |
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| • Check if the external device sent a message |
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| • The header byte of the |
| matched to the protocol and format. |
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| Note |
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| message is not data |
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| • The Q series C24 skips all the messages |
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| needed by the set |
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| transmitted until the header byte set for each |
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| protocol and format. |
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• An external device |
| protocol and format (for example, "ENQ |
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| (05H)" for format 1) is received. |
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transmitted a message |
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| • Check the Q series C24 station No. setting and |
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and "RD" blinked, but | • The Q series C24 |
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| message station No. designation. |
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the Q series C24 did | station No. switch |
| Note |
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not return a response | setting and message |
| • When the station No. designation is local |
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message. ("NEU" | station No. designation |
| station after the header byte set for each |
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remains on and "SD" | do not match. |
| protocol and format is received, the Q series |
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| C24 performs receive processing. |
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does not blink) |
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| • | Set, or shorten, the monitoring time and |
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| retransmit the message from the external |
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| device and determine the trouble from the |
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| contents of the |
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| • The Q series C24 data |
| Note |
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| communications |
| • Error detection by watchdog timers (timer 0 to |
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| monitoring time is set to |
| timer 2) is possible in the following cases. |
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| • When part of a message is skipped. |
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| "infinite", or the |
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| • When transmission from an external device |
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| monitoring time is too |
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| is interrupted. |
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| long. |
| • When a link error was generated while |
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| accessing another station over a |
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| MELSECNET/H, MELSECNET/10. |
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| See Chapter 6 of User's Manual (Application) |
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| for a detailed description of the monitoring time. |
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| • The path setting of the |
| Check the path of the PLC CPU to be accessed |
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| PLC CPU to be |
| and set the path again. |
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| accessed is incorrect. |
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Bidirectional Non procedure
10 - 31 | 10 - 31 |