interfaces — System Interfaces

Module author: Galen Collins <bashwork@gmail.com>

Section author: Galen Collins <bashwork@gmail.com>

API Documentation

Pymodbus Interfaces

A collection of base classes that are used throughout the pymodbus library.

class pymodbus.interfaces.Singleton

Singleton base class http://mail.python.org/pipermail/python-list/2007-July/450681.html

class pymodbus.interfaces.IModbusDecoder

Modbus Decoder Base Class

This interface must be implemented by a modbus message decoder factory. These factories are responsible for abstracting away converting a raw packet into a request / response message object.

decode(message)

Wrapper to decode a given packet

Parameters:message – The raw modbus request packet Returns:The decoded modbus message or None if error

class pymodbus.interfaces.IModbusFramer

A framer strategy interface. The idea is that we abstract away all the detail about how to detect if a current message frame exists, decoding it, sending it, etc so that we can plug in a new Framer object (tcp, rtu, ascii)

addToFrame(message)

Add the next message to the frame buffer

This should be used before the decoding while loop to add the received data to the buffer handle.

Parameters:message – The most recent packet

advanceFrame()

Skip over the current framed message This allows us to skip over the current message after we have processed it or determined that it contains an error. It also has to reset the current frame header handle

buildPacket(message)

Creates a ready to send modbus packet

The raw packet is built off of a fully populated modbus request / response message.

Parameters:message – The request/response to send Returns:The built packet

checkFrame()

Check and decode the next frame

Returns:True if we successful, False otherwise

getFrame()

Get the next frame from the buffer

Returns:The frame data or ‘’

isFrameReady()

Check if we should continue decode logic

This is meant to be used in a while loop in the decoding phase to let the decoder know that there is still data in the buffer.

Returns:True if ready, False otherwise

populateResult(result)

Populates the modbus result with current frame header

We basically copy the data back over from the current header to the result header. This may not be needed for serial messages.

Parameters:result – The response packet

processIncomingPacket(data, callback)

The new packet processing pattern

This takes in a new request packet, adds it to the current packet stream, and performs framing on it. That is, checks for complete messages, and once found, will process all that exist. This handles the case when we read N + 1 or 1 / N messages at a time instead of 1.

The processed and decoded messages are pushed to the callback function to process and send.

Parameters:

• data – The new packet data
• callback – The function to send results to

class pymodbus.interfaces.IModbusSlaveContext

Interface for a modbus slave data context

Derived classes must implemented the following methods:

reset(self) validate(self, fx, address, count=1) getValues(self, fx, address, count=1) setValues(self, fx, address, values)

getValues(fx, address, count=1)

Validates the request to make sure it is in range

Parameters:

• fx – The function we are working with
• address – The starting address
• count – The number of values to retrieve

Returns:

The requested values from a:a+c

reset()

Resets all the datastores to their default values

setValues(fx, address, values)

Sets the datastore with the supplied values

Parameters:

• fx – The function we are working with
• address – The starting address
• values – The new values to be set

validate(fx, address, count=1)

Validates the request to make sure it is in range

Parameters:

• fx – The function we are working with
• address – The starting address
• count – The number of values to test

Returns:

True if the request in within range, False otherwise