PROFIBUS Manual
The diagnostic telegram is divided into several parts. The first 6 bytes and what they mean have been specified in the standard and are fixed. After these 6 mandatory bytes, one or more optional diagnostic blocks then follow. These diagnostic blocks can have different formats.
Diagnostics: telegram with min. 6 and max. 244 bytes PDU
Status1 |
Status2 |
Status3 |
Adr |
Ident H |
Ident L |
Block1 |
Block2 |
The first 6 bytes of diagnostics are decoded according to the following key:
X = value 1 → active, value 0 → inactive
M = slave sends 0, master completes if necessary
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Diagnostic byte 1: status 1 |
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M |
Station_Non_Existent: Station does not exist. This bit is always set to zero by a slave. Here a master notices that this slave is not responding. |
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X |
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Station_Not_ready: Slave is not ready for data exchange. This bit is set by the DP slave if the DP slave is not yet ready for data exchange. |
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X |
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Cfg_Fault: Fault in the configuration telegram. This bit is set by the DP slave, as soon as the configuration data received most recently from the master does not match that detected by the DP slave. |
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X |
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Ext_Diag: An extended diagnosis follows in the telegram. This bit indicates that further diagnostic blocks follow starting from byte 7. |
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X |
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Not_Supported: Requested function is not supported by slave. This bit is set by a slave, as soon as a function is requested that is not supported by this slave. |
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M |
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Invalid_Slave_Response: Invalid response from slave. This bit is always set to zero by a slave. Here a master notices that a slave gives invalid responses. |
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X |
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Prm_Fault: Fault in parameter telegram. This bit is set by the DP slave if the last parameter telegram was faulty. |
M |
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Master_lock: Slave has been locked by another master. This bit is always set to zero by a slave. Here a master notices that this slave has been already locked by another master. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Diagnostic byte 2: status 2 |
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X |
Prm_Req: Slave parameters must be reset. If the DP slave sets this bit, its parameters must be reset followed by reconfiguration. The bit remains set until valid parameters have been implemented. |
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X |
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Stat_Diag: Status diagnostics. If the DP slave sets this bit, the DP master must continue fetching diagnostic data until this bit is deleted again. The DP slave sets this bit when, for example, it is not able to provide any valid user data. |
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1 |
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Permanently at 1, serves to detect protocol errors. |
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X |
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WD_On: Watchdog on. If this bit is set to 1, watchdog monitoring is enabled. |
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X |
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Freeze_Mode: Freeze command received. This bit is set by the DP slave as soon as this DP slave receives the Freeze command. |
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X |
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Sync_Mode: Sync command received. This bit is set by the DP slave as soon as this DP slave receives the Sync command. |
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0 |
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Reserved |
M |
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Deactivated: Slave is deactivated. This bit is always set to zero by a slave. Here a master notices that this slave has been deactivated and should therefore no longer be controlled cyclically. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Diagnostic byte 3: status 3 |
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0 |
0 |
0 |
0 |
0 |
0 |
0 |
Reserved |
X |
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Ext_Diag_Overflow: If this bit is set, more diagnostic information is available than could be transmitted in one telegram. The master must request further diagnosis. |
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Diagnostic byte 4: master address |
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0-125, 255 (0x00-0x7E, 0xFF) |
Address of master after setting parameters Default is 255 (0xFF) |
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If the slave does not have any valid parameters, it sets this value to 255. As soon as valid parameters have been received with a lock from a class 1 master, the address of that master will be entered. It is therefore possible to identify here which master exercises cyclic control over a slave.
7 |
6 |
5 |
4 |
3 |
2 |
1 |
0 |
Diagnostic bytes 5 and 6: Ident number |
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0-255 (0x00-0xFF) |
Ident number high byte |
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0-255 (0x00-0xFF) |
Ident number low byte |
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In these two bytes the slave declares its own Ident_Number.
