pymodbus.constants package

Constants For Modbus Server/Client.

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

class pymodbus.constants.Defaults(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

A collection of modbus default values.

Port

The default modbus tcp server port (502)

TLSPort

The default modbus tcp over tls server port (802)

Backoff

The default exponential backoff delay (0.3 seconds)

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 request.

RetryOnInvalid

A flag indicating if a transaction should be retried in the case that an invalid response is received.

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.

Slave

The modbus slave address. 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 respond).

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-existent slave on a bus will never respond. The client in this case will simply timeout.

broadcast_enable

When False unit_id 0 will be treated as any other unit_id. When True and the unit_id is 0 the server will execute all requests on all server contexts and not respond and the client will skip trying to receive a response. Default value False does not conform to Modbus spec but maintains legacy behavior for existing pymodbus users.

Backoff = 0.3
Baudrate = 19200
BroadcastEnable = False
Bytesize = 8
CloseCommOnError = False
Count = 1
HandleLocalEcho = False
IgnoreMissingSlaves = False
Parity = 'N'
ProtocolId = 0
ReadSize = 1024
ReconnectDelay = 300000
Reconnects = 0
Retries = 3
RetryOnEmpty = False
RetryOnInvalid = False
Slave = 0
Stopbits = 1
Strict = True
TcpPort = 502
Timeout = 3
TlsPort = 802
TransactionId = 0
UdpPort = 502
ZeroMode = False
class pymodbus.constants.DeviceInformation(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

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 optional 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.

Basic = 1
Extended = 3
Regular = 2
Specific = 4
class pymodbus.constants.Endian(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

An enumeration representing the various byte endianness.

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.

Auto = '@'
Big = '>'
Little = '<'
class pymodbus.constants.ModbusPlusOperation(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

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.

ClearStatistics = 4
GetStatistics = 3
class pymodbus.constants.ModbusStatus(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

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

Off = 0
On = 65280
Ready = 0
SlaveOff = 0
SlaveOn = 255
Waiting = 65535
class pymodbus.constants.MoreData(*args, **kwargs)

Bases: pymodbus.interfaces.Singleton

Represents the more follows condition.

Nothing

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

KeepReading

This indicates that there are more objects to be returned.

KeepReading = 255
Nothing = 0

Submodules