Serial Connection Problem

[weizenbierforever]

Hello guys,
I try to connect a simple USB to UART chip from Cypress via the Serial Connection in python3.4 64bit.
RX and TX are shorted, so I recieve a echo with Putty, that already works.

My code:

import visa
visa.log_to_screen()

rm = visa.ResourceManager()
cypresschip = rm.open_resource("COM5")

print(cypresschip.query("123"))

and I get the following Log and Error:

2015-08-11 01:51:32,086 - pyvisa - DEBUG - No user defined library files
2015-08-11 01:51:32,088 - pyvisa - DEBUG - Automatically found library files: ['C:\windows\system32\visa32.dll', 'C:\windows\system32\visa32.dll']
2015-08-11 01:51:32,097 - pyvisa - DEBUG - Library signatures: 90 ok, 0 failed
2015-08-11 01:51:32,097 - pyvisa - DEBUG - Created library wrapper for C:\windows\system32\visa32.dll
2015-08-11 01:51:32,136 - pyvisa - DEBUG - viOpenDefaultRM('<ViObject object at 0x00000000035B9AC8>',) -> 0
2015-08-11 01:51:32,136 - pyvisa - DEBUG - Created ResourceManager with session 4097
2015-08-11 01:51:32,137 - pyvisa - DEBUG - viParseRsrcEx(4097, 'COM5', 'c_ushort(4)', 'c_ushort(5)', <ctypes.c_char_Array_256 object at 0x00000000035B94C8>, <ctypes.c_char_Array_256 object at 0x00000000035B9BC8>, <ctypes.c_char_Array_256 object at 0x00000000035B9C48>) -> 0
2015-08-11 01:51:32,137 - pyvisa - DEBUG - COM5 - opening ...
2015-08-11 01:51:32,157 - pyvisa - DEBUG - viOpen(4097, 'COM5', <AccessModes.no_lock: 0>, 0, '<ViObject object at 0x00000000035B9C48>') -> 0
2015-08-11 01:51:32,158 - pyvisa - DEBUG - COM5 - is open with session 1
2015-08-11 01:51:32,159 - pyvisa - DEBUG - viWrite(1, b'123\r\n', 5, 'c_ulong(5)') -> -1073807298
Traceback (most recent call last):
File "C:\Users\abc\Documents\PythonScripts\python3\Testfiles\SerialPort_test.py", line 17, in
print(cypresschip.query("123"))
File "C:\Anaconda3\lib\site-packages\pyvisa\resources\messagebased.py", line 401, in query
self.write(message)
File "C:\Anaconda3\lib\site-packages\pyvisa\resources\messagebased.py", line 207, in write
count = self.write_raw(message.encode(enco))
File "C:\Anaconda3\lib\site-packages\pyvisa\resources\messagebased.py", line 185, in write_raw
return self.visalib.write(self.session, message)
File "C:\Anaconda3\lib\site-packages\pyvisa\ctwrapper\functions.py", line 1867, in write
ret = library.viWrite(session, data, len(data), byref(return_count))
File "C:\Anaconda3\lib\site-packages\pyvisa\ctwrapper\highlevel.py", line 188, in _return_handler
raise errors.VisaIOError(ret_value)
pyvisa.errors.VisaIOError: VI_ERROR_IO (-1073807298): Could not perform operation because of I/O error.
2015-08-11 01:51:32,168 - pyvisa - DEBUG - COM5 - closing
2015-08-11 01:51:32,169 - pyvisa - DEBUG - viDisableEvent(1, 1073709055, 65535) -> 1073676291
2015-08-11 01:51:32,169 - pyvisa - DEBUG - viDiscardEvents(1, 1073709055, 65535) -> 1073676292
2015-08-11 01:51:32,179 - pyvisa - DEBUG - viClose(1,) -> 0
2015-08-11 01:51:32,179 - pyvisa - DEBUG - COM5 - is closed
2015-08-11 01:51:32,184 - pyvisa - DEBUG - Closing ResourceManager (session: 4097)
2015-08-11 01:51:32,185 - pyvisa - DEBUG - viClose(4097,) -> 0

I also tried to connect directly with the National Measurement and Automation Explorer and got also a IO error.. Till I changed the buffer size for Transmit and Receive Buffer each from 0 to eg 20.
Is there a simmilar Setting in pyvisa? I searched a lot in the source files and did not find anything.
Or is problem related to something else?

Machine Details:
Platform ID: Windows-7-6.1.7601-SP1
Processor: Intel64 Family 6 Model 60 Stepping 3, GenuineIntel

Python:
Implementation: CPython
Executable: C:\Anaconda3\python.exe
Version: 3.4.1
Compiler: MSC v.1600 64 bit (AMD64)
Bits: 64bit
Build: Jun 11 2014 17:27:11 (#default)
Unicode: UCS4

PyVISA Version: 1.8.dev0

Backends:
ni:
Version: 1.8.dev0 (bundled with PyVISA)
#1: C:\windows\system32\visa32.dll:
found by: auto
bitness: 64
Vendor: National Instruments
Impl. Version: 14680064
Spec. Version: 5243904
#2: C:\windows\system32\visa32.dll:
found by: auto
bitness: 64
Vendor: National Instruments
Impl. Version: 14680064
Spec. Version: 5243904

[hgrecco]

As far as I know, the only attribute to control a buffer size in VISA are VI_ATTR_RD_BUF_SIZE and VI_ATTR_WR_BUF_SIZE. But they are only used by formatted I/O operations (viPrintf, viScanf, etc) which are not used by query.

In the VISA documentation there is also a VI_IO_IN_BUF and VI_IO_OUT_BUF which is said to control the Low-level I/O receive/transmit buffers using viSetBuf. But the documentation is very short about it. It might work if you add this to your code (untested):

from visa import constants
rm.visalib.set_buffer(cypresschip.session, constants.VI_IO_IN_BUF, 20)
rm.visalib.set_buffer(cypresschip.session, constants.VI_IO_OUT_BUF, 20)

[weizenbierforever]

This code works for me indeed! Thank you very much! I really appreciate your work!
Here the complete code that works on my system, in case somebody needs it.

import visa
from visa import constants

#visa.log_to_screen()

rm = visa.ResourceManager()
cypresschip = rm.open_resource("COM5")

rm.visalib.set_buffer(cypresschip.session, constants.VI_IO_IN_BUF, 20)
rm.visalib.set_buffer(cypresschip.session, constants.VI_IO_OUT_BUF, 20)

print(cypresschip.query("123abcdefg"))

print(cypresschip.write("123abcdefg"))
print(cypresschip.read())

[hgrecco]

glad to help.

[josecarlosmd]

Hello guys,

I went through the same problem with SIGLENT SPD3303X. The solution was related to termination character. In my case, '\n' for reading and '\0' for writing:

SG = rm.get_instrument('TCPIP0::192.168.1.119::INSTR', read_termination='\n',write_termination='\0')

Hope it helps

[KKIII]

@josecarlosmd - How/where did you find the '\0' terminator for the SIGLENT SPD3303X? I've been struggling with this all day and your post was the solution!
Thanks much

[josecarlosmd]

Sniffing with wireshark!

[KKIII]

Awesome! From: josecarlosmd <notifications@github.com> Sent: Wednesday, January 16, 2019 08:48 To: pyvisa/pyvisa <pyvisa@noreply.github.com> Cc: Kurt Kiesow <kurt.kiesow@gmail.com>; Comment <comment@noreply.github.com> Subject: Re: [pyvisa/pyvisa] Serial Connection Problem (#174) Sniffing with wireshark! — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#174 (comment)> , or mute the thread <https://github.com/notifications/unsubscribe-auth/AEfMOVivRy2JwfQP2mMrj4G5JdrB498_ks5vD1fagaJpZM4FpIhk> . <https://github.com/notifications/beacon/AEfMOf-lL4qToZ3bqVbF2z_g_JxZgvJhks5vD1fagaJpZM4FpIhk.gif>

[johndefiore]

@josecarlosmd I know this is an old thread, but I've been wrestling with the SPD3303X for two days and I finally stumbled on this thread and your solution. Many thanks!!