Exchange bounded M31 Modbus TCP requests

[onehouse] / doc / m31.rst

diff --git a/doc/m31.rst b/doc/m31.rst
index ced2fe2f3489f675c7f93271808b04e149781c30..a1b6eeaa93f9edded98abba95d8e65998e9bed3e 100644 (file)
--- a/doc/m31.rst
+++ b/doc/m31.rst
@@ -25,3 +25,20 @@ capabilities are read-only.
 Tests verify topology and descriptor values without a physical module.
 They do not confirm physical expansion limits or relay timing under
 load. The conservative sixteen-module limit includes the host.
+
+***************
+ Modbus client
+***************
+
+``NewTCPClient`` supplies a caller-owned, serialized connection through
+``Client``. Connect selects the configured unit and has a two-second
+timeout. A request has a one-second write deadline and a two-second
+response deadline, both measured from its start. Caller deadlines and
+cancellation can stop it earlier. Each response must match the
+transaction, unit, function, length, and write acknowledgement.
+Supported functions are 01, 02, 03, 05, 15, and 16. No external Modbus
+package is required.
+
+In-memory stream tests check request bytes, response validation,
+exceptions, truncation, cancellation, and timeouts. They do not verify a
+physical host or TCP network behavior.