Modbus Server: update example description

Extend the example description so that it actually highlights the main
features shown in the example.

Also update the example to match the guidelines:
* Do not use Example in the name
* Update screenshot
* add Connectivity category

Task-number: QTBUG-110890
Pick-to: 6.5
Change-Id: I4eb7603630a9b69fff4cf921b5adff6ea4c125cf
Reviewed-by: André Hartmann <aha_1980@gmx.de>

2 files changed, 62 insertions, 6 deletions

diff --git a/examples/serialbus/modbus/server/doc/images/modbusserver.png b/examples/serialbus/modbus/server/doc/images/modbusserver.png
index 1506382..2bd8cea 100644
--- a/examples/serialbus/modbus/server/doc/images/modbusserver.png
+++ b/examples/serialbus/modbus/server/doc/images/modbusserver.png
diff --git a/examples/serialbus/modbus/server/doc/src/modbusserver.qdoc b/examples/serialbus/modbus/server/doc/src/modbusserver.qdoc
index ec27852..102b565 100644
--- a/examples/serialbus/modbus/server/doc/src/modbusserver.qdoc
+++ b/examples/serialbus/modbus/server/doc/src/modbusserver.qdoc
@@ -1,8 +1,10 @@
-// Copyright (C) 2017 The Qt Company Ltd.
+// Copyright (C) 2023 The Qt Company Ltd.
 // SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
 
 /*! \example modbus/server
-    \title Modbus Server example
+    \title Modbus Server
+    \ingroup qtserialbus-examples
+    \meta category Connectivity
 
     \brief The example implements a Modbus server application.
 
@@ -10,13 +12,67 @@
     adjusts its internal states based on the request and responds with the
     appropriate reply.
 
-    \image ../images/modbusserver.png
-
-    \include examples-run.qdocinc
-
     This example must be used in conjunction with the
     \l {modbus/client}{Modbus Client example}.
     This example should be started and put into the listen state before the
     Modbus client example is started. Subsequent interactions between the two
     examples use the Modbus protocol.
+
+    Key classes used in this example:
+
+    \list
+        \li \l QModbusServer
+        \li \l QModbusDataUnit
+    \endlist
+
+    \image ../images/modbusserver.png
+
+    \section1 Creating a QModbusServer
+
+    An instance of \l QModbusServer is required to perform any communication.
+    Depending on the specified connection type, the example can instantiate a
+    \l QModbusRtuSerialServer (for serial communication) or a
+    \l QModbusTcpServer (for TCP-based communication).
+
+    \snippet modbus/server/mainwindow.cpp create_server_0
+
+    Once the server is created, the register map is set using
+    \l QModbusServer::setMap() method. This register map is used by client
+    applications to read and write server data.
+
+    \snippet modbus/server/mainwindow.cpp create_server_1
+
+    After that the communication parameters and the server address are
+    specified. The communication parameters depend on the communication type:
+
+    \snippet modbus/server/mainwindow.cpp create_server_2
+
+    After the server is created and all the parameters are specified, use
+    \l QModbusServer::connectDevice() to connect to Modbus network.
+
+    \section1 Changing Local Values
+
+    The example allows to change values of all supported
+    \l {QModbusDataUnit::RegisterType}{register types} by using the provided
+    combo boxes or line edits. Once the value is updated in the UI, the
+    \l QModbusServer::setData() method is used to update the actual value on
+    the server:
+
+    \snippet modbus/server/mainwindow.cpp update_data_locally
+
+    \section1 Handling Remote Writes
+
+    The Modbus clients are capable of updating \l {QModbusDataUnit::}{Coils}
+    and \l {QModbusDataUnit::}{HoldingRegisters} by sending write requests.
+    Once the value is updated on the server side using such request, a
+    \l QModbusServer::dataWritten() signal is emitted.
+
+    \snippet modbus/server/mainwindow.cpp connect_data_written
+
+    The Modbus server example connects to this signal, extracts the updated
+    values and updates the UI accordingly:
+
+    \snippet modbus/server/mainwindow.cpp update_data_from_remote
+
+    \include examples-run.qdocinc
 */