how to read data beyond 4096 bytes by VISA

[xiaochouyu]

  hi:

  I can only read 4096 bytes through VISA.I think maybe because the buffer is up to 4096 bytes.

 so how to read data beyond 4096 bytes by VISA?

 thank you!

[Albert.Geven]

Hi

read portions of 4096 bytes of data in a while loop until ready

[xiaochouyu]

Thank you for your reply.

I know to use the LOOP. Can you tell me the specific code?

my code can't work:

Dim fanal As String = ""
Do
status = viRead(vi, strRes, 4096, retCount) 
Dim x As Integer = Val(Mid(strRes, 2, 1))
Dim y As Integer = Val(Mid(strRes, 3, x))
strRes = Mid（strRes， x + 3， y）
fanal = fanal & strRes

Loop Until （retCount < 4096）

read only 16 bytes！

if use

status = viReadToFile(vi, "D:\YouName.WMF", 4096, retCount) 

the result only first viReadToFile can work！

[Albert.Geven]

You probably still have the end character active. For a binary read disable the end character !

[xiaochouyu]

This is the code before reading ,I had disable the end character!Has no effect！

status = viVPrintf(vi, ":SYST:COMM:GPIB:RTER EOI" + vbCrLf, 0) '此命令更改分隔符。

 status = viVPrintf(vi, ":HCOP:DEV:LANG WMF" + vbCrLf, 0) '设置WMF格式

 status = viSetAttribute(vi, VI_ATTR_TMO_VALUE, 20000) '设置超时

status = viVPrintf(vi, ":HCOP:DEST1 'MMEM'" + vbCrLf, 0) '
status = viVPrintf(vi, ":MMEM:NAME 'C:\USER\DATA\FILE.WMF'" + vbCrLf, 0) '

status = viVPrintf(vi, ":HCOP" + vbCrLf, 0) '开始

  status = viVPrintf(vi, ":MMEM:MSIS 'C’" + vbCrLf, 0) '

status = viVPrintf(vi, ":MMEM:CDIR '\USER\DATA\'" + vbCrLf, 0) '
status = viVPrintf(vi, ":MMEM:DATA? 'FILE.WMF'" + vbCrLf, 0) '

[patrick.o]

xiaochouyu,

Thanks for posting on our forums. There are several reasons why you may not be able to read more than 4096 bytes. I would recommend looking at the article below for more information. It may help you determine the root of the issue.

VISA Read on a Serial Device Does not Return the Requested Number of Bytes

https://knowledge.ni.com/KnowledgeArticleDetails?id=kA00Z0000019KrvSAE

[xiaochouyu]

thanks

"the amount of data that it returns depends on 3 important details about your settings and your serial data: your termination character, the amount of data requested, and the timeout period."

I'm not sure then termination character is termination EOI? and can you gave me a VB.NET code?

The following section is I found from the official website of the instrument.and I am writing code based on this：

10 REM Set the termination EOI

20 IEC TERM 1

30 IEC OUT 20,"SYST:COMM:GPIB:RTER EOI"

40 REM Change the hardcopy language to WMF

50 IEC OUT 20,"HCOP:DEV:LANG WMF"

60 REM Change the hardcopy port to file

70 IEC OUT 20,"HCOP:DEST1 'MMEM'"

80 REM Set the file name

90 IEC OUT 20,"MMEM:NAME 'C:\USER\DATA\FILE.WMF'"

100 REM Make the hardcopy

110 IEC OUT 20,"HCOP;*WAI"

130 REM Set the path to hard disk c:

140 IEC OUT 20,"MMEM:MSIS 'C'"

150 REM Set the path

160 IEC OUT 20,"MMEM:CDIR '\USER\DATA\'"

170 REM Put the file in the output buffer

180 IEC OUT 20,"MMEM:DATA? 'FILE.WMF'"

190 REM The file is transferred with an header. 第一个标记是“#”

200 REM The next sign indicates how many signs will follow

210 REM now with the information how large the file is without header

220 REM So a header looks like '#43210' and will be removed by the

230 REM next steps.

240 REM Get the file out of the buffer

250 IEC IN 20,S$

270 X=VAL(MID$(S$,2,1))

280 Z=VAL(MID$(S$,3,X))

290 T$=MID$(S$,X+3,Z)

300 REM Open a file as output

310 OPENO# 1,"A:\HARDCOPY.WMF"

320 REM Save the WMF data to this file

330 PRINT# 1,T$

340 END

[patrick.o]

xiaochouyu,

Just to clarify a few things, are you using NI's VISA driver to interface with your instrument using .NET code in VisualBasic? Also, are you using a third-party instrument?

If my assumptions are correct, and you are using NI VISA in VisualBasic, you can find reference documentation by following the instructions in the link below:

Creating a .NET Application without Measurement Studio

http://zone.ni.com/reference/en-XX/help/370131S-01/ni-visa/creatingnetapplicationwithoutmeasurements...

I would also recommend you go over the information in the NI VISA driver help documentation here. I hope this helps.

[xiaochouyu]

thanks

  In addition to the screenshot function not implemented, other functions have been implemented. Now there is only a problem with the screenshot. I can be sure that the instrument can be programmed using VB.net.