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s7: explain V1-initial firmware-band fallback to users #721

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s7: explain V1-initial firmware-band fallback to users #721

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9 changes: 8 additions & 1 deletion s7/connection.py
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Original file line number Diff line number Diff line change
Expand Up @@ -205,7 +205,14 @@ def connect(
if self._server_session_version is not None:
self._session_setup_ok = self._setup_session()
else:
logger.warning("PLC did not provide ServerSessionVersion - session setup incomplete")
logger.warning(
"PLC did not provide a scalar ServerSessionVersion attribute. "
"This is the V1-initial S7-1200 firmware band (FW < 4.5 "
"predating TLS) which sends a Struct(314) value and requires "
"the proprietary SessionKey handshake — not yet implemented "
"in python-snap7 (tracked in issue #710). Falling back to "
"legacy PUT/GET: db_read/db_write will work, browse() will not."
)
self._session_setup_ok = False

# Step 6: Version-specific post-setup
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