NI PCI 485/8

[K C]

I am not the expert. It just happens that I use ModBus and I use the RS-485 board and....

About the data comming back I am lost right now but I will think about it

Do you use the ModBus lib from NI ? Is it possible to build your own VI's for talking to the ModBus device. I don't use this library. I build my own VI's for communication with the ModBus devices also because we have a few dedicated commands.

Maybe you can build a faster interface this way. You can always try this with repeating one command to see how fast it can work.

[azwhoony]

Last time I found an example without using NI library. Unfortunately..I still get the same time interval 200ms transmiting modbus frame from labview to port. I will test and see about the quantity register.

Thanks.

[K C]

When I send characters with my 485/2 board the only delay I see is the time the program is doing something else then sending data.

Can you try to send data with a small VI.

Try this for data: 0108 0000 8844 8638 it is the ModBus loopback command for a slave at address 1. Your ModBus device should respond with the same data. In your case this means triple data 

[azwhoony]

Hi KC.

I've tried that and I still get 200ms to finish 1 modbus query and response. Some of my device does not support 08 function. I'll try to work on the register quantity, play around with the baudrate and see if there's any different.

But I get a new problem!! There's another device giving me wrong value at certain register. I use mantissa & exp to translate the response from modbus HEX value. At the device screen..it shows -0.1 but we get xFF80 0000 which is -Inf. Just for this register(phase angle register) we get this value. Do you have any idea what's going on?

Thanks.

[K C]

I don't understand where the 200msec is comming from. Can you post the VI that you used to test this ?

The value as such doesn't say anything you have to know how you device is building up this number. Should be in the manual.