Serial comms: Delay between Read & Write

[Tarun]

Hi Joshua,

Thanks, I tried it out, set and flushed the receive and the write buffers, but still no joy. 😞

[dblj]

Has anyone found a work around for this delay problem?

I have the exact same problem with a couple minor diffs.

When I do a basic read and write on my RS-485 line (using Labview VISA) I have a 2.7msec delay between the read and write.  Unfortunately in my application I need to write in a window of 2msec after the read or else I overlap.

RS-485, 115.2k baud rate

I'm using labview 8.0

WinXP Pro

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[Tarun]

Hi,

Wow! This was a long time back. 

I was using LV7.1 at the time.

To improve my Read-Write turn around times, I was given a beta version update of VISA by National Instruments that improved it to around ±2ms (can't remember the exact time).  I had VISA 3.0 at the time.  I assume that those updates are included in LV8.0.

I don't think you will be able to get better than 2.7ms, but I could be wrong.  I stand to be corrected.

Jerry

[JoseRamon]

Hello !

I have a very similar problem with one aplication that read-write the serial port. I need to read a hex character "0x11" and just after (minus than 5 ms) I have to send some data (20 characters). The problem is I put one time loop of 1 ms and just when I read the character that I want to read I go out  from the time loop and I send the data, but I have been watching the osciloscope and My transmision is around 30 ms after I read the "0x11" and I want 5 ms after.

I also tried to put the VISA write inside the time loop and tx just after that It read the 0x11 b ut when I go to watch it in the osciloscope I can watch that there are  a delay of  30 ms aproximately.

I dont know how can I do it in real time, maybe someone can explain my something that I can do.

Thank for your attention nad I sorry for my English but I do the best that I know.

[Albert.Geven]

Hi JoseRamon

To really make this work you need to get rid of windows. This alone already can give you timing jitter of more than 10 ms.
maybe an idea to offload this to a single cip proceesor (like atmel or pic) and do the non time critical stuff on a pc.

[samriddh]

Hi TARUN,

Can you tell me how to use NI Spy for trouble shooting of Serial Communication.

I am dealing with the same kind of problem as you had in yeater years.

Thanks & Regards,

Samriddh Sarbalhi