HP 4277a reading only one byte

[JMcgeever]

Hi,

I am trying to simultaneously communicate with a HP 4277a LCZ meter and a Keithley 595 quastistatic CV meter. When I use the function VISA read purely on the HP 4277a, the response is the full expected string. However, when I stack the GPIB cables on top of each other to communicate with both instruments, the read response is only one byte (one character). Is there any way I can fix this?

Thanks

[santo_13]

Can you share a simple code that is causing this problem?

[JMcgeever]

Hi,

Sorry for the late reply.

Below is the block diagram, and the front panel for when there is only the 4277a connected to the computer and when the 4277a and the 595 are both connected. As you can see from the indicator, only one byte is sent through when both are connected.

Thanks.

[GerdW]

Hi JM,

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@JMcgeever wrote:

Below is the block diagram…

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Well, no error handling and a coercion dot with this little part of the block diagram…

How do you configure and open the communication port?

You need to provide more information than just some small images! (We cannot edit/run/debug images with LabVIEW…)

[JMcgeever]

Hi GerdW,

Thanks for your reply! 

I've only made this block diagram to demonstrate what the issue is. 

As for configuring the communication port I'm not 100% sure what you mean by that (I'm new to LABview sorry!). I run tests through the NI MAX software, where I query the instrument and it returns only one byte. I have attached the test vi; by writing A2 to the instrument the chosen function is to read capacitance.

Thanks!

JM

[GerdW]

Hi JM,

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@JMcgeever wrote:

I run tests through the NI MAX software, where I query the instrument and it returns only one byte.

I have attached the test vi; by writing A2 to the instrument the chosen function is to read capacitance.

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What does the manual say about the format of command messages?

Does your device need any "end of line" chars?

(Most devices I had to work with needed LF or CR chars, some also accepted the semicolon…)

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@JMcgeever wrote:

As for configuring the communication port I'm not 100% sure what you mean by that (I'm new to LABview sorry!).

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Which port do you use at all?

Is there any configuration done in MAX?

As you are new to LabVIEW: there are Training resources offered at the top of the LabVIEW board…

(We can judge you are new because you even spell LabVIEW wrong! 😄 )

[JMcgeever · Accepted solution]

Hi GerdW,

There is no configuration done in NI MAX, however I think that shouldn't matter as it works when there is only the 4277a connected. As it is a relatively old machine (Believe it's from the 80's) this could be an innate issue. 

The manual does not say you need a termination character at the end of a line.

In terms of the port, I simply select the VISA resource name and connect it to the VISA resource input of the VISA read and the VISA write functions.

Thanks,

JM

[JMcgeever · Accepted solution]

From what I understand, the issue is a problem with older machines. The 595 has slightly different GPIB interface functions to that of the 4277a and is therefore incompatible, resulting in only one byte being read. 

Thanks for the help!