[modbus_controller] courtesy response (#10027)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>
Co-authored-by: pre-commit-ci-lite[bot] <117423508+pre-commit-ci-lite[bot]@users.noreply.github.com>

esphome/components/modbus/modbus.cpp

@@ -66,7 +66,10 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
   uint8_t data_offset = 3;
 
   // Per https://modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf Ch 5 User-Defined function codes
-  if (((function_code >= 65) && (function_code <= 72)) || ((function_code >= 100) && (function_code <= 110))) {
+  if (((function_code >= FUNCTION_CODE_USER_DEFINED_SPACE_1_INIT) &&
+       (function_code <= FUNCTION_CODE_USER_DEFINED_SPACE_1_END)) ||
+      ((function_code >= FUNCTION_CODE_USER_DEFINED_SPACE_2_INIT) &&
+       (function_code <= FUNCTION_CODE_USER_DEFINED_SPACE_2_END))) {
     // Handle user-defined function, since we don't know how big this ought to be,
     // ideally we should delegate the entire length detection to whatever handler is
     // installed, but wait, there is the CRC, and if we get a hit there is a good
@@ -91,10 +94,14 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
   } else {
     // data starts at 2 and length is 4 for read registers commands
     if (this->role == ModbusRole::SERVER) {
-      if (function_code == 0x1 || function_code == 0x3 || function_code == 0x4 || function_code == 0x6) {
+      if (function_code == ModbusFunctionCode::READ_COILS ||
+          function_code == ModbusFunctionCode::READ_DISCRETE_INPUTS ||
+          function_code == ModbusFunctionCode::READ_HOLDING_REGISTERS ||
+          function_code == ModbusFunctionCode::READ_INPUT_REGISTERS ||
+          function_code == ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
         data_offset = 2;
         data_len = 4;
-      } else if (function_code == 0x10) {
+      } else if (function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
         if (at < 6) {
           return true;
         }
@@ -104,7 +111,10 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
       }
     } else {
       // the response for write command mirrors the requests and data starts at offset 2 instead of 3 for read commands
-      if (function_code == 0x5 || function_code == 0x06 || function_code == 0xF || function_code == 0x10) {
+      if (function_code == ModbusFunctionCode::WRITE_SINGLE_COIL ||
+          function_code == ModbusFunctionCode::WRITE_SINGLE_REGISTER ||
+          function_code == ModbusFunctionCode::WRITE_MULTIPLE_COILS ||
+          function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
         data_offset = 2;
         data_len = 4;
       }
@@ -112,7 +122,7 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
 
     // Error ( msb indicates error )
     // response format:  Byte[0] = device address, Byte[1] function code | 0x80 , Byte[2] exception code, Byte[3-4] crc
-    if ((function_code & 0x80) == 0x80) {
+    if ((function_code & FUNCTION_CODE_EXCEPTION_MASK) == FUNCTION_CODE_EXCEPTION_MASK) {
       data_offset = 2;
       data_len = 1;
     }
@@ -143,10 +153,10 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
     if (device->address_ == address) {
       found = true;
       // Is it an error response?
-      if ((function_code & 0x80) == 0x80) {
+      if ((function_code & FUNCTION_CODE_EXCEPTION_MASK) == FUNCTION_CODE_EXCEPTION_MASK) {
         ESP_LOGD(TAG, "Modbus error function code: 0x%X exception: %d", function_code, raw[2]);
         if (waiting_for_response != 0) {
-          device->on_modbus_error(function_code & 0x7F, raw[2]);
+          device->on_modbus_error(function_code & FUNCTION_CODE_MASK, raw[2]);
         } else {
           // Ignore modbus exception not related to a pending command
           ESP_LOGD(TAG, "Ignoring Modbus error - not expecting a response");
@@ -154,12 +164,14 @@ bool Modbus::parse_modbus_byte_(uint8_t byte) {
         continue;
       }
       if (this->role == ModbusRole::SERVER) {
-        if (function_code == 0x3 || function_code == 0x4) {
+        if (function_code == ModbusFunctionCode::READ_HOLDING_REGISTERS ||
+            function_code == ModbusFunctionCode::READ_INPUT_REGISTERS) {
           device->on_modbus_read_registers(function_code, uint16_t(data[1]) | (uint16_t(data[0]) << 8),
                                            uint16_t(data[3]) | (uint16_t(data[2]) << 8));
           continue;
         }
-        if (function_code == 0x6 || function_code == 0x10) {
+        if (function_code == ModbusFunctionCode::WRITE_SINGLE_REGISTER ||
+            function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
           device->on_modbus_write_registers(function_code, data);
           continue;
         }
@@ -199,7 +211,7 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
 
   // Only check max number of registers for standard function codes
   // Some devices use non standard codes like 0x43
-  if (number_of_entities > MAX_VALUES && function_code <= 0x10) {
+  if (number_of_entities > MAX_VALUES && function_code <= ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
     ESP_LOGE(TAG, "send too many values %d max=%zu", number_of_entities, MAX_VALUES);
     return;
   }
@@ -210,15 +222,17 @@ void Modbus::send(uint8_t address, uint8_t function_code, uint16_t start_address
   if (this->role == ModbusRole::CLIENT) {
     data.push_back(start_address >> 8);
     data.push_back(start_address >> 0);
-    if (function_code != 0x5 && function_code != 0x6) {
+    if (function_code != ModbusFunctionCode::WRITE_SINGLE_COIL &&
+        function_code != ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
       data.push_back(number_of_entities >> 8);
       data.push_back(number_of_entities >> 0);
     }
   }
 
   if (payload != nullptr) {
-    if (this->role == ModbusRole::SERVER || function_code == 0xF || function_code == 0x10) {  // Write multiple
+    if (this->role == ModbusRole::SERVER || function_code == ModbusFunctionCode::WRITE_MULTIPLE_COILS ||
-      data.push_back(payload_len);  // Byte count is required for write
+        function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {  // Write multiple
+      data.push_back(payload_len);                                        // Byte count is required for write
     } else {
       payload_len = 2;  // Write single register or coil
     }

esphome/components/modbus/modbus.h

@@ -3,6 +3,8 @@
 #include "esphome/core/component.h"
 #include "esphome/components/uart/uart.h"
 
+#include "esphome/components/modbus/modbus_definitions.h"
+
 #include <vector>
 
 namespace esphome {
@@ -65,12 +67,12 @@ class ModbusDevice {
     this->parent_->send(this->address_, function, start_address, number_of_entities, payload_len, payload);
   }
   void send_raw(const std::vector<uint8_t> &payload) { this->parent_->send_raw(payload); }
-  void send_error(uint8_t function_code, uint8_t exception_code) {
+  void send_error(uint8_t function_code, ModbusExceptionCode exception_code) {
     std::vector<uint8_t> error_response;
     error_response.reserve(3);
     error_response.push_back(this->address_);
-    error_response.push_back(function_code | 0x80);
+    error_response.push_back(function_code | FUNCTION_CODE_EXCEPTION_MASK);
-    error_response.push_back(exception_code);
+    error_response.push_back(static_cast<uint8_t>(exception_code));
     this->send_raw(error_response);
   }
   // If more than one device is connected block sending a new command before a response is received

esphome/components/modbus/modbus_definitions.h

@@ -0,0 +1,86 @@
+#pragma once
+
+#include "esphome/core/component.h"
+
+namespace esphome {
+namespace modbus {
+
+/// Modbus definitions from specs:
+/// https://modbus.org/docs/Modbus_Application_Protocol_V1_1b3.pdf
+// 5 Function Code Categories
+const uint8_t FUNCTION_CODE_USER_DEFINED_SPACE_1_INIT = 65;  // 0x41
+const uint8_t FUNCTION_CODE_USER_DEFINED_SPACE_1_END = 72;   // 0x48
+
+const uint8_t FUNCTION_CODE_USER_DEFINED_SPACE_2_INIT = 100;  // 0x64
+const uint8_t FUNCTION_CODE_USER_DEFINED_SPACE_2_END = 110;   // 0x6E
+
+enum class ModbusFunctionCode : uint8_t {
+  CUSTOM = 0x00,
+  READ_COILS = 0x01,
+  READ_DISCRETE_INPUTS = 0x02,
+  READ_HOLDING_REGISTERS = 0x03,
+  READ_INPUT_REGISTERS = 0x04,
+  WRITE_SINGLE_COIL = 0x05,
+  WRITE_SINGLE_REGISTER = 0x06,
+  READ_EXCEPTION_STATUS = 0x07,   // not implemented
+  DIAGNOSTICS = 0x08,             // not implemented
+  GET_COMM_EVENT_COUNTER = 0x0B,  // not implemented
+  GET_COMM_EVENT_LOG = 0x0C,      // not implemented
+  WRITE_MULTIPLE_COILS = 0x0F,
+  WRITE_MULTIPLE_REGISTERS = 0x10,
+  REPORT_SERVER_ID = 0x11,               // not implemented
+  READ_FILE_RECORD = 0x14,               // not implemented
+  WRITE_FILE_RECORD = 0x15,              // not implemented
+  MASK_WRITE_REGISTER = 0x16,            // not implemented
+  READ_WRITE_MULTIPLE_REGISTERS = 0x17,  // not implemented
+  READ_FIFO_QUEUE = 0x18,                // not implemented
+};
+
+/*Allow  comparison operators between ModbusFunctionCode and uint8_t*/
+inline bool operator==(ModbusFunctionCode lhs, uint8_t rhs) { return static_cast<uint8_t>(lhs) == rhs; }
+inline bool operator==(uint8_t lhs, ModbusFunctionCode rhs) { return lhs == static_cast<uint8_t>(rhs); }
+inline bool operator!=(ModbusFunctionCode lhs, uint8_t rhs) { return !(static_cast<uint8_t>(lhs) == rhs); }
+inline bool operator!=(uint8_t lhs, ModbusFunctionCode rhs) { return !(lhs == static_cast<uint8_t>(rhs)); }
+inline bool operator<(ModbusFunctionCode lhs, uint8_t rhs) { return static_cast<uint8_t>(lhs) < rhs; }
+inline bool operator<(uint8_t lhs, ModbusFunctionCode rhs) { return lhs < static_cast<uint8_t>(rhs); }
+inline bool operator<=(ModbusFunctionCode lhs, uint8_t rhs) { return static_cast<uint8_t>(lhs) <= rhs; }
+inline bool operator<=(uint8_t lhs, ModbusFunctionCode rhs) { return lhs <= static_cast<uint8_t>(rhs); }
+inline bool operator>(ModbusFunctionCode lhs, uint8_t rhs) { return static_cast<uint8_t>(lhs) > rhs; }
+inline bool operator>(uint8_t lhs, ModbusFunctionCode rhs) { return lhs > static_cast<uint8_t>(rhs); }
+inline bool operator>=(ModbusFunctionCode lhs, uint8_t rhs) { return static_cast<uint8_t>(lhs) >= rhs; }
+inline bool operator>=(uint8_t lhs, ModbusFunctionCode rhs) { return lhs >= static_cast<uint8_t>(rhs); }
+
+// 4.3 MODBUS Data model
+enum class ModbusRegisterType : uint8_t {
+  CUSTOM = 0x00,
+  COIL = 0x01,
+  DISCRETE_INPUT = 0x02,
+  HOLDING = 0x03,
+  READ = 0x04,
+};
+
+// 7 MODBUS Exception Responses:
+const uint8_t FUNCTION_CODE_MASK = 0x7F;
+const uint8_t FUNCTION_CODE_EXCEPTION_MASK = 0x80;
+
+enum class ModbusExceptionCode : uint8_t {
+  ILLEGAL_FUNCTION = 0x01,
+  ILLEGAL_DATA_ADDRESS = 0x02,
+  ILLEGAL_DATA_VALUE = 0x03,
+  SERVICE_DEVICE_FAILURE = 0x04,
+  ACKNOWLEDGE = 0x05,
+  SERVER_DEVICE_BUSY = 0x06,
+  MEMORY_PARITY_ERROR = 0x08,
+  GATEWAY_PATH_UNAVAILABLE = 0x0A,
+  GATEWAY_TARGET_DEVICE_FAILED_TO_RESPOND = 0x0B,
+};
+
+// 6.12 16 (0x10) Write Multiple registers:
+const uint8_t MAX_NUM_OF_REGISTERS_TO_WRITE = 123;  // 0x7B
+
+// 6.3 03 (0x03) Read Holding Registers
+// 6.4 04 (0x04) Read Input Registers
+const uint8_t MAX_NUM_OF_REGISTERS_TO_READ = 125;  // 0x7D
+/// End of Modbus definitions
+}  // namespace modbus
+}  // namespace esphome

esphome/components/modbus_controller/__init__.py

@@ -20,6 +20,7 @@ from .const import (
     CONF_BYTE_OFFSET,
     CONF_COMMAND_THROTTLE,
     CONF_CUSTOM_COMMAND,
+    CONF_ENABLED,
     CONF_FORCE_NEW_RANGE,
     CONF_MAX_CMD_RETRIES,
     CONF_MODBUS_CONTROLLER_ID,
@@ -28,8 +29,11 @@ from .const import (
     CONF_ON_OFFLINE,
     CONF_ON_ONLINE,
     CONF_REGISTER_COUNT,
+    CONF_REGISTER_LAST_ADDRESS,
     CONF_REGISTER_TYPE,
+    CONF_REGISTER_VALUE,
     CONF_RESPONSE_SIZE,
+    CONF_SERVER_COURTESY_RESPONSE,
     CONF_SKIP_UPDATES,
     CONF_VALUE_TYPE,
 )
@@ -49,6 +53,7 @@ ModbusController = modbus_controller_ns.class_(
 )
 
 SensorItem = modbus_controller_ns.struct("SensorItem")
+ServerCourtesyResponse = modbus_controller_ns.struct("ServerCourtesyResponse")
 ServerRegister = modbus_controller_ns.struct("ServerRegister")
 
 ModbusFunctionCode_ns = modbus_controller_ns.namespace("ModbusFunctionCode")
@@ -143,6 +148,14 @@ ModbusOfflineTrigger = modbus_controller_ns.class_(
 
 _LOGGER = logging.getLogger(__name__)
 
+SERVER_COURTESY_RESPONSE_SCHEMA = cv.Schema(
+    {
+        cv.Optional(CONF_ENABLED, default=False): cv.boolean,
+        cv.Optional(CONF_REGISTER_LAST_ADDRESS, default=0xFFFF): cv.hex_uint16_t,
+        cv.Optional(CONF_REGISTER_VALUE, default=0): cv.hex_uint16_t,
+    }
+)
+
 ModbusServerRegisterSchema = cv.Schema(
     {
         cv.GenerateID(): cv.declare_id(ServerRegister),
@@ -162,6 +175,7 @@ CONFIG_SCHEMA = cv.All(
             cv.Optional(
                 CONF_COMMAND_THROTTLE, default="0ms"
             ): cv.positive_time_period_milliseconds,
+            cv.Optional(CONF_SERVER_COURTESY_RESPONSE): SERVER_COURTESY_RESPONSE_SCHEMA,
             cv.Optional(CONF_MAX_CMD_RETRIES, default=4): cv.positive_int,
             cv.Optional(CONF_OFFLINE_SKIP_UPDATES, default=0): cv.positive_int,
             cv.Optional(
@@ -232,7 +246,7 @@ def validate_modbus_register(config):
 
 
 def _final_validate(config):
-    if CONF_SERVER_REGISTERS in config:
+    if CONF_SERVER_COURTESY_RESPONSE in config or CONF_SERVER_REGISTERS in config:
         return modbus.final_validate_modbus_device("modbus_controller", role="server")(
             config
         )
@@ -299,6 +313,20 @@ async def to_code(config):
     var = cg.new_Pvariable(config[CONF_ID])
     cg.add(var.set_allow_duplicate_commands(config[CONF_ALLOW_DUPLICATE_COMMANDS]))
     cg.add(var.set_command_throttle(config[CONF_COMMAND_THROTTLE]))
+    if server_courtesy_response := config.get(CONF_SERVER_COURTESY_RESPONSE):
+        cg.add(
+            var.set_server_courtesy_response(
+                cg.StructInitializer(
+                    ServerCourtesyResponse,
+                    ("enabled", server_courtesy_response[CONF_ENABLED]),
+                    (
+                        "register_last_address",
+                        server_courtesy_response[CONF_REGISTER_LAST_ADDRESS],
+                    ),
+                    ("register_value", server_courtesy_response[CONF_REGISTER_VALUE]),
+                )
+            )
+        )
     cg.add(var.set_max_cmd_retries(config[CONF_MAX_CMD_RETRIES]))
     cg.add(var.set_offline_skip_updates(config[CONF_OFFLINE_SKIP_UPDATES]))
     if CONF_SERVER_REGISTERS in config:

esphome/components/modbus_controller/const.py

@@ -2,6 +2,7 @@ CONF_ALLOW_DUPLICATE_COMMANDS = "allow_duplicate_commands"
 CONF_BITMASK = "bitmask"
 CONF_BYTE_OFFSET = "byte_offset"
 CONF_COMMAND_THROTTLE = "command_throttle"
+CONF_ENABLED = "enabled"
 CONF_OFFLINE_SKIP_UPDATES = "offline_skip_updates"
 CONF_CUSTOM_COMMAND = "custom_command"
 CONF_FORCE_NEW_RANGE = "force_new_range"
@@ -13,8 +14,11 @@ CONF_ON_ONLINE = "on_online"
 CONF_ON_OFFLINE = "on_offline"
 CONF_RAW_ENCODE = "raw_encode"
 CONF_REGISTER_COUNT = "register_count"
+CONF_REGISTER_LAST_ADDRESS = "register_last_address"
 CONF_REGISTER_TYPE = "register_type"
+CONF_REGISTER_VALUE = "register_value"
 CONF_RESPONSE_SIZE = "response_size"
+CONF_SERVER_COURTESY_RESPONSE = "server_courtesy_response"
 CONF_SKIP_UPDATES = "skip_updates"
 CONF_USE_WRITE_MULTIPLE = "use_write_multiple"
 CONF_VALUE_TYPE = "value_type"

esphome/components/modbus_controller/modbus_controller.cpp

@@ -112,6 +112,12 @@ void ModbusController::on_modbus_read_registers(uint8_t function_code, uint16_t
            "0x%X.",
            this->address_, function_code, start_address, number_of_registers);
 
+  if (number_of_registers == 0 || number_of_registers > modbus::MAX_NUM_OF_REGISTERS_TO_READ) {
+    ESP_LOGW(TAG, "Invalid number of registers %d. Sending exception response.", number_of_registers);
+    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_ADDRESS);
+    return;
+  }
+
   std::vector<uint16_t> sixteen_bit_response;
   for (uint16_t current_address = start_address; current_address < start_address + number_of_registers;) {
     bool found = false;
@@ -136,9 +142,21 @@ void ModbusController::on_modbus_read_registers(uint8_t function_code, uint16_t
     }
 
     if (!found) {
-      ESP_LOGW(TAG, "Could not match any register to address %02X. Sending exception response.", current_address);
+      if (this->server_courtesy_response_.enabled &&
-      send_error(function_code, 0x02);
+          (current_address <= this->server_courtesy_response_.register_last_address)) {
-      return;
+        ESP_LOGD(TAG,
+                 "Could not match any register to address 0x%02X, but default allowed. "
+                 "Returning default value: %d.",
+                 current_address, this->server_courtesy_response_.register_value);
+        sixteen_bit_response.push_back(this->server_courtesy_response_.register_value);
+        current_address += 1;  // Just increment by 1, as the default response is a single register
+      } else {
+        ESP_LOGW(TAG,
+                 "Could not match any register to address 0x%02X and default not allowed. Sending exception response.",
+                 current_address);
+        this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_ADDRESS);
+        return;
+      }
     }
   }
 
@@ -156,27 +174,27 @@ void ModbusController::on_modbus_write_registers(uint8_t function_code, const st
   uint16_t number_of_registers;
   uint16_t payload_offset;
 
-  if (function_code == 0x10) {
+  if (function_code == ModbusFunctionCode::WRITE_MULTIPLE_REGISTERS) {
     number_of_registers = uint16_t(data[3]) | (uint16_t(data[2]) << 8);
-    if (number_of_registers == 0 || number_of_registers > 0x7B) {
+    if (number_of_registers == 0 || number_of_registers > modbus::MAX_NUM_OF_REGISTERS_TO_WRITE) {
       ESP_LOGW(TAG, "Invalid number of registers %d. Sending exception response.", number_of_registers);
-      send_error(function_code, 3);
+      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
       return;
     }
     uint16_t payload_size = data[4];
     if (payload_size != number_of_registers * 2) {
       ESP_LOGW(TAG, "Payload size of %d bytes is not 2 times the number of registers (%d). Sending exception response.",
                payload_size, number_of_registers);
-      send_error(function_code, 3);
+      this->send_error(function_code, ModbusExceptionCode::ILLEGAL_DATA_VALUE);
       return;
     }
     payload_offset = 5;
-  } else if (function_code == 0x06) {
+  } else if (function_code == ModbusFunctionCode::WRITE_SINGLE_REGISTER) {
     number_of_registers = 1;
     payload_offset = 2;
   } else {
     ESP_LOGW(TAG, "Invalid function code 0x%X. Sending exception response.", function_code);
-    send_error(function_code, 1);
+    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_FUNCTION);
     return;
   }
 
@@ -211,7 +229,7 @@ void ModbusController::on_modbus_write_registers(uint8_t function_code, const st
   if (!for_each_register([](ServerRegister *server_register, uint16_t offset) -> bool {
         return server_register->write_lambda != nullptr;
       })) {
-    send_error(function_code, 1);
+    this->send_error(function_code, ModbusExceptionCode::ILLEGAL_FUNCTION);
     return;
   }
 
@@ -220,7 +238,7 @@ void ModbusController::on_modbus_write_registers(uint8_t function_code, const st
         int64_t number = payload_to_number(data, server_register->value_type, offset, 0xFFFFFFFF);
         return server_register->write_lambda(number);
       })) {
-    send_error(function_code, 4);
+    this->send_error(function_code, ModbusExceptionCode::SERVICE_DEVICE_FAILURE);
     return;
   }
 
@@ -431,8 +449,15 @@ void ModbusController::dump_config() {
                 "ModbusController:\n"
                 "  Address: 0x%02X\n"
                 "  Max Command Retries: %d\n"
-                "  Offline Skip Updates: %d",
+                "  Offline Skip Updates: %d\n"
-                this->address_, this->max_cmd_retries_, this->offline_skip_updates_);
+                "  Server Courtesy Response:\n"
+                "    Enabled: %s\n"
+                "    Register Last Address: 0x%02X\n"
+                "    Register Value: %d",
+                this->address_, this->max_cmd_retries_, this->offline_skip_updates_,
+                this->server_courtesy_response_.enabled ? "true" : "false",
+                this->server_courtesy_response_.register_last_address, this->server_courtesy_response_.register_value);
+
 #if ESPHOME_LOG_LEVEL >= ESPHOME_LOG_LEVEL_VERBOSE
   ESP_LOGCONFIG(TAG, "sensormap");
   for (auto &it : this->sensorset_) {

esphome/components/modbus_controller/modbus_controller.h

@@ -16,35 +16,9 @@ namespace modbus_controller {
 
 class ModbusController;
 
-enum class ModbusFunctionCode {
+using modbus::ModbusFunctionCode;
-  CUSTOM = 0x00,
+using modbus::ModbusRegisterType;
-  READ_COILS = 0x01,
+using modbus::ModbusExceptionCode;
-  READ_DISCRETE_INPUTS = 0x02,
-  READ_HOLDING_REGISTERS = 0x03,
-  READ_INPUT_REGISTERS = 0x04,
-  WRITE_SINGLE_COIL = 0x05,
-  WRITE_SINGLE_REGISTER = 0x06,
-  READ_EXCEPTION_STATUS = 0x07,   // not implemented
-  DIAGNOSTICS = 0x08,             // not implemented
-  GET_COMM_EVENT_COUNTER = 0x0B,  // not implemented
-  GET_COMM_EVENT_LOG = 0x0C,      // not implemented
-  WRITE_MULTIPLE_COILS = 0x0F,
-  WRITE_MULTIPLE_REGISTERS = 0x10,
-  REPORT_SERVER_ID = 0x11,               // not implemented
-  READ_FILE_RECORD = 0x14,               // not implemented
-  WRITE_FILE_RECORD = 0x15,              // not implemented
-  MASK_WRITE_REGISTER = 0x16,            // not implemented
-  READ_WRITE_MULTIPLE_REGISTERS = 0x17,  // not implemented
-  READ_FIFO_QUEUE = 0x18,                // not implemented
-};
-
-enum class ModbusRegisterType : uint8_t {
-  CUSTOM = 0x0,
-  COIL = 0x01,
-  DISCRETE_INPUT = 0x02,
-  HOLDING = 0x03,
-  READ = 0x04,
-};
 
 enum class SensorValueType : uint8_t {
   RAW = 0x00,     // variable length
@@ -256,6 +230,12 @@ class SensorItem {
   bool force_new_range{false};
 };
 
+struct ServerCourtesyResponse {
+  bool enabled{false};
+  uint16_t register_last_address{0xFFFF};
+  uint16_t register_value{0};
+};
+
 class ServerRegister {
   using ReadLambda = std::function<int64_t()>;
   using WriteLambda = std::function<bool(int64_t value)>;
@@ -530,6 +510,12 @@ class ModbusController : public PollingComponent, public modbus::ModbusDevice {
   void set_max_cmd_retries(uint8_t max_cmd_retries) { this->max_cmd_retries_ = max_cmd_retries; }
   /// get how many times a command will be (re)sent if no response is received
   uint8_t get_max_cmd_retries() { return this->max_cmd_retries_; }
+  /// Called by esphome generated code to set the server courtesy response object
+  void set_server_courtesy_response(const ServerCourtesyResponse &server_courtesy_response) {
+    this->server_courtesy_response_ = server_courtesy_response;
+  }
+  /// Get the server courtesy response object
+  ServerCourtesyResponse get_server_courtesy_response() const { return this->server_courtesy_response_; }
 
  protected:
   /// parse sensormap_ and create range of sequential addresses
@@ -572,6 +558,9 @@ class ModbusController : public PollingComponent, public modbus::ModbusDevice {
   CallbackManager<void(int, int)> online_callback_{};
   /// Server offline callback
   CallbackManager<void(int, int)> offline_callback_{};
+  /// Server courtesy response
+  ServerCourtesyResponse server_courtesy_response_{
+      .enabled = false, .register_last_address = 0xFFFF, .register_value = 0};
 };
 
 /** Convert vector<uint8_t> response payload to float.

tests/components/modbus_controller/common.yaml

@@ -45,6 +45,22 @@ modbus_controller:
           printf("address=%d, value=%d", x);
           return true;
     max_cmd_retries: 0
+  - id: modbus_controller4
+    modbus_id: mod_bus2
+    address: 0x4
+    server_courtesy_response:
+      enabled: true
+      register_last_address: 100
+      register_value: 0
+    server_registers:
+      - address: 0x0001
+        value_type: U_WORD
+        read_lambda: |-
+          return 0x8;
+      - address: 0x0005
+        value_type: U_WORD
+        read_lambda: |-
+          return (random_uint32() % 100);
 binary_sensor:
   - platform: modbus_controller
     modbus_controller_id: modbus_controller1