readCoils method

@override Future<Uint8List> readCoils(int slaveId, int address, int quantity)

Read coil status (FC 01).

Reads from 1 to 2000 contiguous coils in a remote device.

Parameters:

• slaveId: The slave device ID (1-247)
• address: Starting address of coils
• quantity: Number of coils to read (1-2000)

Returns: Byte array with coil status (bit-packed)

Example:

final coils = await client.readCoils(1, 0, 10);
final isCoil0On = (coils[0] & 0x01) != 0;

Implementation

@override
Future<Uint8List> readCoils(int slaveId, int address, int quantity) async {
  if (slaveId < _addressMin || slaveId > _addressMax) {
    throw ArgumentError(
        'modbus: slaveId \'$slaveId\' must be between \'$_addressMin\' and \'$_addressMax\'');
  }
  if (quantity < readBitsQuantityMin || quantity > readBitsQuantityMax) {
    throw ArgumentError(
        'modbus: quantity \'$quantity\' must be between \'$readBitsQuantityMin\' and \'$readBitsQuantityMax\'');
  }

  final response = await send(
    slaveId,
    ProtocolDataUnit(
      funcCodeReadCoils,
      uint16ToBytes([address, quantity]),
    ),
  );

  if (response.data.length - 1 != response.data[0]) {
    throw Exception(
        'modbus: response byte size \'${response.data.length - 1}\' does not match count \'${response.data[0]}\'');
  }
  if (response.data[0] != (quantity + 7) ~/ 8) {
    throw Exception(
        'modbus: response byte size \'${response.data[0]}\' does not match quantity to bytes \'${(quantity + 7) ~/ 8}\'');
  }

  return Uint8List.fromList(response.data.sublist(1));
}