On ProfibusDP network during initialization, the PLC (master) always asks slaves for diagnostic data (get_diagnostic telegram).
The slave will respond with diagnostic data.
Diagnostic data can consist of:
- standard diagnostic or
- standard diagnostic + extended diagnostic
The length of standard diagnostic data is fixed, while extended diagnostic data is manufacturer-specific, and its content and length are defined by the manufacturer.
TeSysT serves not only standard diagnostic but also extended diagnostic (manufacturer-specific) telegrams. The maximum length of a diagnostic telegram from TeSysT is 36bytes. The description of the vzTeSysT diagnostic telegram is in the attachment.
In Control Expert or older Unity software, the Profibus modules allocate 32 bytes by default for diagnostic telegram, which is not enough for TeSysT. It must be increased to 36 bytes or more.

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