core/homeassistant/components/modbus/services.yaml

write_coil:
  description: Write to a modbus coil.
  fields:
    address:
      description: Address of the register to write to.
      example: 0
    state:
      description: State to write.
      example: false
    unit:
      description: Address of the modbus unit.
      example: 21
    hub:
      description: Optional Modbus hub name. A hub with the name 'default' is used if not specified.
      example: "hub1"
write_register:
  description: Write to a modbus holding register.
  fields:
    address:
      description: Address of the holding register to write to.
      example: 0
    unit:
      description: Address of the modbus unit.
      example: 21
    value:
      description: Value (single value or array) to write.
      example: "0 or [4,0]"
    hub:
      description: Optional Modbus hub name. A hub with the name 'default' is used if not specified.
      example: "hub1"