# `constants` — Modbus Default Values

## API Documentation

### Constants For Modbus Server/Client

This is the single location for storing default values for the servers and clients.

class `pymodbus.constants.``Defaults`

  A collection of modbus default values

  `Port`

    The default modbus tcp server port (502)

  `Retries`

    The default number of times a client should retry the given request before failing (3)

  `RetryOnEmpty`

    A flag indicating if a transaction should be retried in the case that an empty response is received. This is useful for slow clients that may need more time to process a requst.

  `Timeout`

    The default amount of time a client should wait for a request to be processed (3 seconds)

  `Reconnects`

    The default number of times a client should attempt to reconnect before deciding the server is down (0)

  `TransactionId`

    The starting transaction identifier number (0)

  `ProtocolId`

    The modbus protocol id. Currently this is set to 0 in all but proprietary implementations.

  `UnitId`

    The modbus slave addrss. Currently this is set to 0x00 which means this request should be broadcast to all the slave devices (really means that all the devices should respons).

  `Baudrate`

    The speed at which the data is transmitted over the serial line. This defaults to 19200.

  `Parity`

    The type of checksum to use to verify data integrity. This can be on of the following:

        - (E)ven - 1 0 1 0 | P(0)
        - (O)dd  - 1 0 1 0 | P(1)
        - (N)one - 1 0 1 0 | no parity

    This defaults to (N)one.

  `Bytesize`

    The number of bits in a byte of serial data. This can be one of 5, 6, 7, or 8. This defaults to 8.

  `Stopbits`

    The number of bits sent after each character in a message to indicate the end of the byte. This defaults to 1.

  `ZeroMode`

    Indicates if the slave datastore should use indexing at 0 or 1. More about this can be read in section 4.4 of the modbus specification.

  `IgnoreMissingSlaves`

    In case a request is made to a missing slave, this defines if an error should be returned or simply ignored. This is useful for the case of a serial server emulater where a request to a non-existant slave on a bus will never respond. The client in this case will simply timeout.

class `pymodbus.constants.``ModbusStatus`

  These represent various status codes in the modbus protocol.

  `Waiting`

    This indicates that a modbus device is currently waiting for a given request to finish some running task.

  `Ready`

    This indicates that a modbus device is currently free to perform the next request task.

  `On`

    This indicates that the given modbus entity is on

  `Off`

    This indicates that the given modbus entity is off

  `SlaveOn`

    This indicates that the given modbus slave is running

  `SlaveOff`

    This indicates that the given modbus slave is not running

class `pymodbus.constants.``Endian`

  An enumeration representing the various byte endianess.

  `Auto`

    This indicates that the byte order is chosen by the current native environment.

  `Big`

    This indicates that the bytes are in little endian format

  `Little`

    This indicates that the bytes are in big endian format

  Note

  I am simply borrowing the format strings from the python struct module for my convenience.

class `pymodbus.constants.``ModbusPlusOperation`

  Represents the type of modbus plus request

  `GetStatistics`

    Operation requesting that the current modbus plus statistics be returned in the response.

  `ClearStatistics`

    Operation requesting that the current modbus plus statistics be cleared and not returned in the response.

class `pymodbus.constants.``DeviceInformation`

  Represents what type of device information to read

  `Basic`

    This is the basic (required) device information to be returned. This includes VendorName, ProductCode, and MajorMinorRevision code.

  `Regular`

    In addition to basic data objects, the device provides additional and optinoal identification and description data objects. All of the objects of this category are defined in the standard but their implementation is optional.

  `Extended`

    In addition to regular data objects, the device provides additional and optional identification and description private data about the physical device itself. All of these data are device dependent.

  `Specific`

    Request to return a single data object.

class `pymodbus.constants.``MoreData`

  Represents the more follows condition

  `Nothing`

    This indiates that no more objects are going to be returned.

  `KeepReading`

    This indicates that there are more objects to be returned.