N109X-Series Oscilloscope with acquisition limit test

This Python example uses an N109X-series DCA-M oscilloscope to perform an eye measurement (bit rate) on channel 6A. The programs performs the following tasks:

Places FlexDCA to its default settings. This places the FlexDCA triggering to front panel which is required to view a valid eye diagram, and then makes all the required setting to view an eye diagram.
Queries the N109X to see if it supports pattern locking (option PLK) and then turns on pattern locking if available.
Returns the measured trigger rate that is input to the N109X.
Runs an acquisition limit test and then activates the bit-rate measurement on the data.

About the :TRIGger:MRATe? query

The :TRIGger:MRATe? query returns the baud rate of the N109X’s clock input signal. For this query to work, at least one of the N109X’s input channels must be turned on, but a signal does not need to be connected to the channel. Also, the N109X’s data acquisition must be in Run mode, or, if in single mode, a single acquisition must first be run to ensure valid data for the measurement.

To run this program

Run this program on a PC that has FlexDCA running. In the following listing, FlexDCA is identified by the red text: localhost.

If you change localhost to an N1000A, you can run the program on a PC to control FlexDCA on an N1000A. Connect the N109X to the N1000A.

Install an N109X-series oscilloscope to FlexDCA’s slot 6. Change the DCAMSLT constant if you want to use a different slot.
Data in is expected to be 10.3125 GBd, but you can change this to any acceptable rate for the oscilloscope.
Connect valid signal to channel 6A on the N1090X.
Connect a clock to the N1090X’s Clock In.
Display an eye diagram on FlexDCA.

Example Script

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DCA-M-eye-meas.py

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# -*- coding: utf-8 -*-
""" Demonstrates measurements on DCA-M oscilloscope.
- Requres a N109X-series DCA-M oscilloscope with valid eye diagram displayed.
- Change the CHANNEL constant to match your setup.
- ADDRESS constant is set for FlexDCA and DCA-M on PC.
- Change ADDRESS constant to DCA-X's address if DCA-M is connected
to the DCA-X.
Data in is expected to be 10.3125 Gb/s, but you can change this
to any acceptable rate for the oscilloscope.
The default setup command places the DCA-M triggering to front
panel which is required to view a valid eye diagram.
"""
import pyvisa as visa  # import VISA library
ADDRESS = 'TCPIP0::localhost::hislip0,4880::INSTR'
#ADDRESS = 'TCPIP0::K-N1000A-00003::hislip0,4880::INSTR'
CHANNEL = '5A'  # N109X's channel


def open_flexdca_connection(address):
    """ Opens visa connection to FlexFlexDCA. """
    print('Connecting to Flexdca ...')
    try:
        rm = visa.ResourceManager()
        connection = rm.open_resource(address)
        connection.timeout = 20000  # Set connection timeout to 20s
        connection.read_termination = '\n'
        connection.write_termination = '\n'
        inst_id = connection.query('*IDN?')
        print('\nFlexDCA connection established to:\n' + inst_id, flush=True)
        connection.write(':SYSTem:DEFault')
        connection.query('*OPC?')
    except (visa.VisaIOError, visa.InvalidSession):
        print('\nVISA ERROR: Cannot open instrument address.\n', flush=True)
        return None
    except Exception as other:
        print('\nVISA ERROR: Cannot connect to instrument:', other, flush=True)
        print('\n')
        return None
    return connection


def show_module_information(FlexDCA, channel):
    """ Queries information from the DCA-M. Returns a string
    of DCA-M's options. """
    slot = channel[0]
    print('\nDCA-M Device ID: ', FlexDCA.query(':EMODules:DCAM' + slot + ':DEVice?'))
    print('DCA-M model: ', FlexDCA.query(':SYSTem:MODel? SLOT' + slot))
    print('Options: ', FlexDCA.query(':SYSTem:OPTions? SLOT' + slot))
    print('Trigger source: ', FlexDCA.query(':SLOT' + slot + ':TRIGger:SOURce?'))
    clockrate = FlexDCA.query(':SLOT' + slot + ':TRIG:MRATe?')
    if '-1.00' in clockrate or '0.00' in clockrate:
        print('ERROR: DCA-M is not triggered. Check inputs.')
    else:
        print('Measured clock rate: ', clockrate)


def return_scalar(FlexDCA, query):
    """ Returns a FlexDCA scalar measurement result. """
    import time

    class ScalarMeasQuestionableException(Exception):
        """ A scalar measurement result is questionable. """
        pass

    class ScalarMeasTimeOutException(Exception):
        """ A scalar measurement has timed out. """
        pass

    timeout = FlexDCA.timeout / 1000  # convert ms to s
    query = query.strip('?')
    start_time = time.time()  # time in seconds
    while(True):
        time.sleep(0.2)
        status = FlexDCA.query(query + ':STATus?')
        if 'CORR' in status:  # valid measurement result
            return FlexDCA.query(query + '?')  # get measurement
        elif 'QUES' in status:  # questionable results
            s = query + '\nReason: ' + FlexDCA.query(query + ':STATus:REASon?')
            raise ScalarMeasQuestionableException(s)
        elif (int(time.time() - start_time)) > timeout:  # IO timout
            s = query + '\nReason: ' + FlexDCA.query(query + ':STATus:REASon?')
            raise ScalarMeasTimeOutException(s)


def make_measurements(FlexDCA, slot):
    """ Displays four measurements in FlexDCA's results panel.
    Returns the result of each measurement. """
    FlexDCA.write(':MEASure:EYE:LIST:CLEar')
    FlexDCA.write(':MEASure:EYE:BITRate')
    FlexDCA.write(':MEASure:EYE:FALLtime')
    FlexDCA.write(':MEASure:EYE:RISetime')
    FlexDCA.write(':MEASure:EYE:AMPLitude')
    print('-' * 20, '\nMeasured:')
    meas = return_scalar(FlexDCA, ':MEASure:EYE:BITRate?')
    print('Eye Bit Rate: ' + meas + ' b/s')
    meas = return_scalar(FlexDCA, ':MEASure:EYE:FALLtime?')
    print('Fall Time: ' + meas + 's')
    meas = return_scalar(FlexDCA, ':MEASure:EYE:RISetime?')
    print('Rise Time: ' + meas + 's')
    meas = return_scalar(FlexDCA, ':MEASure:EYE:AMPLitude?')
    print('Eye Amplitude: ' + meas)


FlexDCA = open_flexdca_connection(ADDRESS)
show_module_information(FlexDCA, CHANNEL)
print('Acquiring data...')
make_measurements(FlexDCA, CHANNEL[0])
FlexDCA.write(':SYSTem:GTLocal')
FlexDCA.close()