Port manager

From SweepMe! Wiki
Jump to: navigation, search

SweepMe! supports and simplifies communication to devices via RS232 (COM port), GPIB, USB and TCPIP by using the SweepMe! Port manager.

Introduction

The communication with the hardware is usually done in each Device Class. In order to simplify the process of creating the communication channel, i.e. establish a connection, SweepMe! provides the port manager for easy handling.

Supported protocols

  • COM: standard PC serial port using RS-232 protocol
  • GPIB: an IEEE-488-Bus, a standard communication
  • TCPIP: in planning
  • USB: plug and play USB test and measurement device as supported by pyvisa
  • VB: a National Instrument VirtualBench device

Usage

Configuration

The following variables have to be set within the __init__ function of a Device Class:

In order to get the available ports listed in the GUI of the corresponding Module, choose desired port types by:

self.port_types = ["COM", "GPIB", "USB", "VB"]

A port object is automatically created by

self.port_manager = True


Port properties

You can set port properties during __init__ of the Device Class or before connect() is called by modifying the self.port_properties dictionary. In order to see all keys of the dictionary, use

print(self.port_properties)


These parameters can be changed through

self.port_properties = {
    "baudrate" : 9600, 
    "EOL": "\n",
    ...
}

or change a parameter of self.port_properties as done in the the following example

self.port_properties["EOL"] = "\r"

Some important and commonly used parameters are explained here:

Command Interface Type Default value Explanation
EOL COM String "\n" "End of line"-character, will be added to each command sent by self.port.write() and defines the end of each message read by self.port.read()
EOLwrite COM String None replaces the character which will be added to each command sent by self.port.write()
EOLread COM String None replace the character which defines the end of each message read by self.port.read()
baudrate COM Integer 9600 The Baudrate defines the speed of the COM port communication, must be identical to the value of the instrument
bytesize COM Integer 8 length of one byte, must be identical to value of the instrument
stopbyte COM Integer 1
parity COM String "N"
xonxoff COM bool False
rtscts COM bool False
dsrdtr COM bool False
rts COM bool True
dtr COM bool True
raw_write COM bool False send the argument as is without further unicode encoding, an eol/terminator-character is still added if specified.
raw_read COM bool False receive the answer as is without further unicode decoding
timeout COM, USB, GPIB Float 1.0 time in seconds before a timeout error is raised
delay COM, GPIB Float 0.0 delay time in seconds after writing a command to allow an instrument to process the current command.

Communication

If the port manager is activated, the port is automatically available within all functions of the sequencer procedure as the variable:

self.port

A message can be sent byusing:

self.port.write("string of the message without end-of-line/terminator character")

The end-of-line character ("EOL") will be set by changing the port properties

The answer of a device is acquired by:

var = self.port.read()

The returned object is typically a string, so please do not forget to change the type if needed by using e.g. int() or float().

In case you need direct access to the port object created by the port manager, use:

self.port.port

Thus, you can use commmands as defined by pyserial for COM port communication or pyvisa for GPIB/USB communication.

Terminator / End-of-Line character for GPIB

Typically, communication via GPIB does not require to set an end-of-line (EOL) character. However, some devices expect and send special characters at the end of each message indicating that the command/message is complete.

At the moment, setting EOL for GPIB is not implemented via self.port_properties. One has to modify the pyvisa GPIBInstrument object, using

self.port.port.write_termination = "\r\n"
self.port.port.read_termination = "\r\n"
# "\r\n" is here one example for using Carriage Return (CR) and Line Feed (LF) as terminator

which can be done e.g. in the connect() function of the DeviceClass


COM port

In order to check the number of already received bytes, you can use:

number_of_received_bytes = self.port.in_waiting()

As SweepMe! is based on python 3, all strings that are send via self.port.write() are actually unicode strings. The Port Manager automatically converts them to bytes before sending them using the library pyserial. Similarly, received bytes are automatically converted back to unicode strings. If you like to have raw access to the bytes that are sent and received, please use the port properties 'raw_read' and 'raw_write'.