Add support for SDMXXX energy meters (#1260)

Co-authored-by: Jesse Hills <3060199+jesserockz@users.noreply.github.com>

esphome/components/modbus/__init__.py

@@ -1,7 +1,9 @@
 import esphome.codegen as cg
 import esphome.config_validation as cv
+from esphome.cpp_helpers import gpio_pin_expression
 from esphome.components import uart
-from esphome.const import CONF_ID, CONF_ADDRESS
+from esphome.const import CONF_FLOW_CONTROL_PIN, CONF_ID, CONF_ADDRESS
+from esphome import pins
 
 DEPENDENCIES = ["uart"]
 
@@ -15,6 +17,7 @@ CONFIG_SCHEMA = (
     cv.Schema(
         {
             cv.GenerateID(): cv.declare_id(Modbus),
+            cv.Optional(CONF_FLOW_CONTROL_PIN): pins.gpio_output_pin_schema,
         }
     )
     .extend(cv.COMPONENT_SCHEMA)
@@ -29,6 +32,10 @@ async def to_code(config):
 
     await uart.register_uart_device(var, config)
 
+    if CONF_FLOW_CONTROL_PIN in config:
+        pin = await gpio_pin_expression(config[CONF_FLOW_CONTROL_PIN])
+        cg.add(var.set_flow_control_pin(pin))
+
 
 def modbus_device_schema(default_address):
     schema = {