RTS/CTS Problem ?

[Nok]

Hi..
I have to communicate between RS485 (NI card) to RS485 of the application board "with handshaking RTS/CTS"

I use serial VISA of labview and set Flow Control = RTS/CTS. and I monitor the status of RTS and CTS by property node to LED.

I espect that when I run my program first RTS should be green but it always red (no signal when I measure from Oscilloscope).

When I connect with the board, CTS is green and I can receive some wrong data from the board !!

I don't understand firstly, why the status of RTS is always red ? Is this behavior is correct ?

Thanks for any kind help.

[Dan_Mondrik]

If you are using RTS/CTS flow control, you should not be looking at the RTS state. It will always return -1. Depending on how you handle the -1 case, I could believe your LED would be either green or red (I know you said it is red) but it will never change color.

The driver itself will properly set the state of RTS, but it's just not something we allow you to monitor, because you are not directly in control of it. If you measured the RTS signal from the pin with an oscilloscope, you should see it change when you write data with VISA Write.

CTS, on the other hand, should always be returning a valid value. If CTS is set, your device is telling you that you have data to read. And if you get garbage, perhaps your instrument is not properly set up in RT
S/CTS mode?

Dan Mondrik
National Instruments

[Nok]

Thanks Dan,

First of all, The program I use come from the vendor of my application board in which he mention that The RTS state (which use property node to indicate the status to LED) should be green until the data is full in the buffer and then change to RED.

But when I run it on my PC, I can get the correct result but just the LED didn't be sth I espect.


I understand from your text that, RTS state can't moniter, Is it right ?

So, I should not take this behavior into account if the result is already correct ?


Thanks in advance

[Dan_Mondrik]

It is correct that you can't monitor RTS while using RTS/CTS flow control. So if the LED color for the RTS indicator is the only thing that isn't working as expected, then you have nothing to worry about.

Dan Mondrik