Serial port buffer flush question

[MileP]

I'm trying to use VISA Flush I/O Buffer Function to flush serial port receive/transmit buffers without I/O operation.

As per the help, mask value (0x40 | 0x80) flushes both transmit and receive buffers without I/O operation.

But it seems the flush doesn't work. Did I use this function correctly?

[JÞB]

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@MileP wrote:

I'm trying to use VISA Flush I/O Buffer Function to flush serial port receive/transmit buffers without I/O operation.

As per the help, mask value (0x40 | 0x80) flushes both transmit and receive buffers without I/O operation.

But it seems the flush doesn't work. Did I use this function correctly?

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Probably YES!

Usually I get to say words to the effect of "Yes, you may have done that wrong"  In this case I susupect that you are dealing with a "chatty Cathy" UART or terminal emulator that just keeps shoveling data onto the port.

SO, what's on the other end?

[MileP]

I'm using RS232 for the serial port communication between the LabVIEW application and target.

It has handshake state and data transmit/receive state. If handshake state is complete, it transits to data transmit/receive state.

I want to clean up everything in the serial port transmit/receive buffer after handshake state is complete, so the next state won't have any overhead.

As per help, I thought VISA Flush I/O Buffer Function with mask value 0xC0 would do the clean up without I/O operation.

[KyleTTU]

Hi MileP, 

Can you explain what you mean by it doesn't seem to be working correctly?

Regards, 

Kyle S

[MileP]

I expect the flush would discard all the data in the serial port transmit/receive buffers and no I/O operation,

but I saw the data were still transmitted on NI Spy. So I think it did the flush but also did the I/O operation.

[KyleTTU]

Hi MileP, 

If possible could you try the Windows Flush Com Buffers.vi?  It can be found in ...\LabVIEW...\vi.lib\instr\_sersup.llb.  This vi is a Windows based vi and I'm curious if it will work for you. 

Regards, 

Kyle S

[MileP]

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@KyleTTU wrote:

Hi MileP, 

If possible could you try the Windows Flush Com Buffers.vi?  It can be found in ...\LabVIEW...\vi.lib\instr\_sersup.llb.  This vi is a Windows based vi and I'm curious if it will work for you. 

Regards, 

Kyle S

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Do you mean a VI called "Windows Flush Com Buffers"? I can't find it. But I saw "VISA Flush I/O Buffer" at many places. They are all same, right?

[KyleTTU]

This one actually acts just a little bit differently which is why I want to try it.  Otherwise can we attempt to not do a full transmit to the device and instead just query it with a *IDN? command, then flush the buffer.  I am curious about this handshaking and if you are continously getting data from the other end when attempting to flush the buffer.

Regards,

Kyle S