Modbus operations

ModbusUnit exposes the standard Modbus operations. Register reads return list[int]. Bit reads return list[bool].

# Register I/O
await unit.read_holding_registers(address, count)  # FC03
await unit.read_input_registers(address, count)  # FC04
await unit.write_register(address, value)  # FC06
await unit.write_registers(address, values)  # FC16

# Coils and discrete inputs
await unit.read_coils(address, count)  # FC01
await unit.read_discrete_inputs(address, count)  # FC02
await unit.write_coil(address, value)  # FC05
await unit.write_coils(address, values)  # FC15

The interface also includes exception status (FC07), diagnostics (FC08), comm-event counter and log (FC11/FC12), report-server-id (FC17), file records (FC20/FC21), mask-write (FC22), read/write-registers (FC23), FIFO queue (FC24), and device identification (FC43/14). The reference lists every method with its signature and function code.

All operations raise on failure. See Exceptions for the error hierarchy.

Decoding what you read

Register reads return raw 16-bit words. modbus_connection.decode converts them to Python values:

from modbus_connection.decode import decode_float32, decode_int16, decode_string

decode_int16(await unit.read_holding_registers(9, 1))
decode_float32(await unit.read_holding_registers(40, 2))
decode_string(await unit.read_holding_registers(10, 4))

modbus_connection.encode performs the inverse conversion for writes. Both modules support signed and unsigned integers, floats, and strings, with configurable word order for multi-register values. decode additionally covers network addresses (IPv4, IPv6, EUI-48). The reference lists every function.

For a device with more than a handful of values, use the device-modelling framework instead. It attaches these conversions to fields and pools the reads.