UnicodeDecodeError: 'ascii' codec can't decode byte 0xfe

Hi All,

I am trying to, a) connect to a signal generator (Agilent N5182A MXG) that supports ASCII range(256) using TCPIP. b) set a signal waveform to the signal generator

Unfortunately I am unable to set the waveform. Apparently the error shows that it supports only ASCII range(128) but not the extended ASCII range(129-256). The ‘0xfe’ comes in the extended ASCII set.

Have anyone faced this problem? Is there a syntax to specify the encoding method pyvisa should use?

The error,

SK@PC:~/ubuntu/pyvisa$ python sg_pyvisa_simple.py
Traceback (most recent call last):
  File "sg_pyvisa_simple.py", line 89, in <module>
    inst_sg.write(set_waveform)
  File "/opt/anaconda2/lib/python2.7/site-packages/pyvisa/resources/messagebased.py", line 202, in write
    if message.endswith(term):
UnicodeDecodeError: 'ascii' codec can't decode byte 0xfe in position 94: ordinal not in range(128)

Attaching a) The script that produced the above error

import visa
import numpy
import itertools
import pylab as pl
import math

#######################################
# Variables
#######################################

IP_SG = '10.10.100.131'
siggen_filename ='myCombSig'
num_tone=16
num_smpl_tone=32 

#######################################
# Initialization
#######################################

rm = visa.ResourceManager('@py')

#######################################
# Helper Functions
#######################################

def df_open_connection(rm, ip):
	inst = rm.open_resource('TCPIP::'+ ip + '::INSTR')
	return inst

def df_close_connection(inst):
	inst.close()

def df_my_range(start, end, step):
	while start <= end:
		yield start
		start += step

def df_Comb_sig_gen(num_tone, num_smpl_tone):
	comb_real = []
	comb_imag = []
	comb_cmpx = []
	M = num_tone * num_smpl_tone
	N = 0
	C = num_tone
	k = pl.frange(float(-(C - 1)) / 2, float((C - 1)) / 2, 1)
	for n in df_my_range(-N + 1, M + N - 2, 1):
		cc = numpy.exp(2j * math.pi * k * numpy.array(n) / (C))
		comb_cmpx.append(numpy.sum(cc))  

	return (comb_cmpx)

def df_set_waveform(comb_signal, filename):

	scale  = numpy.amax([numpy.amax(comb_signal.real),numpy.amax(comb_signal.imag)])

	comb_signal_real_scale = numpy.array(comb_signal.real)/scale
	comb_signal_imag_scale = numpy.array(comb_signal.imag)/scale

	i = comb_signal_real_scale
	q = comb_signal_imag_scale

	i_dac = map(lambda x: int((x+32767) % 32767), i)
	q_dac = map(lambda x: int((x+32767) % 32767), q)

	iq_str = ""

	for i_val, q_val in itertools.izip(i_dac, q_dac):
		iq_str += chr((i_val >> 8) & 0x00FF) #32766 (0x7FFE) -> 7F
		iq_str += chr(i_val & 0x00FF)		 #32766 (0x7FFE) -> FE, error when writing FE
		iq_str += chr((q_val >> 8) & 0x00FF)
		iq_str += chr(q_val & 0x00FF)

	scpi_command = ':MEM:DATA "WFM1:{}",#{}{}{}\n'.format(filename.upper(), len(str(len(iq_str))), str(len(iq_str)), iq_str)

	return scpi_command

#################################################
# Action: To Set a Waveform on Signal Generator
#################################################

inst_sg = df_open_connection(rm, IP_SG)
inst_sg.write(':FREQ 1.8825 GHz; POWer -30DBM')

comb_signal = df_Comb_sig_gen(float(num_tone),float(num_smpl_tone))	
comb_signal = numpy.array(comb_signal)

set_waveform = df_set_waveform(comb_signal, siggen_filename)

inst_sg.write(set_waveform)

df_close_connection(inst_sg)`

b) The output of “python -m visa info”

Machine Details:
   Platform ID:    Linux-4.4.0-92-generic-x86_64-with-debian-stretch-sid
   Processor:      x86_64

Python:
   Implementation: CPython
   Executable:     /opt/anaconda2/bin/python
   Version:        2.7.12
   Compiler:       GCC 4.4.7 20120313 (Red Hat 4.4.7-1)
   Bits:           64bit
   Build:          Jul  2 2016 17:42:40 (#default)
   Unicode:        UCS4

PyVISA Version: 1.8

Backends:
   ni:
      Version: 1.8 (bundled with PyVISA)
      #1: /usr/lib/x86_64-linux-gnu/libvisa.so.0.0.0:
         found by: auto
         bitness: 64
         Could not get more info:
            VI_ERROR_NSUP_ATTR (-1073807331): The specified attribute is not defined or supported by the referenced object.
   py:
      Version: 0.3.dev0
      ASRL INSTR: Available via PySerial (3.4)
      TCPIP INSTR: Available 
      USB RAW: Available via PyUSB (1.0.2). Backend: N/A
      USB INSTR: Available via PyUSB (1.0.2). Backend: N/A
      GPIB INSTR:
         Please install linux-gpib to use this resource type.
         No module named gpib
      TCPIP SOCKET: Available 
   sim:
      Version: 0.3
      Spec version: 1.1

If any other logs need to be produced to study the above issue, kindly share the syntax and I shall revert with the appropriate logs. Thanks for your help.

[MatthieuDartiailh]

At least your message get through now.

[svanan77]

Ok, the below works.

inst_sg.write_binary_values(':MEM:DATA "WFM1:{}",'.format(filename.upper()), iq_str, datatype='c')

Thanks Matthieu for your time.