Instrument Control (GPIB, Serial, VISA, IVI)
VISA Read (Serial) Latency in LabVIEW Real Time
mikeeeee wrote:Hi,
How long does it take for a VISA Read (serial port RS232) operation to be completed in LabVIEW Real Time, say I try to read 8 bits?
Can this operation be completed within 0.2ms? Where can I find such performance benchmark?
In the event that this is not possible, what is the next best solution? I know on a Windows machine, I can only measure performance down to 1ms and not better than that. I hope in RT this is not the case and the timer resolution is better?
Thanks in advance!
I know you don't want to hear "it depends", but it does. Baud Rate. Clock Speed. Limitations of the UART. Program Latency. If we want to get down to the molecular level, skin effect and hole trapping come into play. 
Of those things, Real Time will help with Latency.
At a high Baud Rate, such as 115.2k, you should be able to read 8 bits in 0.2ms in the hardware.
The resolution of Real Time is microseconds. So you're right, your only chance of benchmarking this would be with Real Time.
I typed my response then read your question again, and what I think I missed was, you want to know how long the Function takes, once the bytes are available at the port?
You should be able to expect it to occur in less than 0.2mS. Even on a non-RT system, i think it would be less than 0.2mS, but you couldn't verify it. Put 10 of these reads in a for loop and try measuring that on a non-RT. I bet it's less than 2mS.
