Gotchas

Use this page only for library-specific caveats.

Shared SLMP setup, profile, point-limit, and end-code symptoms live in the shared SLMP Troubleshooting & Codes page. For profile limits and device availability, use the shared SLMP Profile Parameters page.

Current library-specific caveats

Area	Symptom	Guidance
IPv6 endpoint	Client construction rejects an IPv6 literal, or connection fails because a hostname has no IPv4 result.	Sync and async TCP/UDP clients are IPv4-only. Use an IPv4 literal or a hostname with an IPv4 result; the first IPv4 result is used and there is no IPv6 fallback.
Request ordering	Several callers share one client.	Ordinary sync and async clients process valid operations in FIFO order. Async cancellation while queued removes that operation without sending; close() rejects the active and queued generation. Do not add a second queue wrapper.
Aggregate size	read_named or poll exceeds one random-read request.	The complete plan is rejected before transport. Split it into explicit application calls and define the required snapshot/consistency behavior.
Ambiguous write result	A state-changing operation fails after send may have started.	Catch SlmpOutcomeUnknownError, inspect reason and cause, verify PLC state, and do not retry blindly.
Malformed ACK	An ACK-only API raises SlmpOutcomeUnknownError with reason PROTOCOL.	The PLC returned unexpected success data or another response-identity defect. The transport has been retired; reconcile PLC state before opening a new generation. Use raw_command() only for an intentionally data-bearing vendor command.

values = await asyncio.gather(
    read_typed(client, "D100", "U"),
    read_typed(client, "D101", "U"),
)