Am I allowed to wire the transmit lines of two RS-485 boards on two machines in parrallel provided I make sure they nver try to transmitt at the same time?

[Ben]

Hi All,

I am devloping an app that needs to talk to a custom made device using full-duplex rs-485. There are two types of operations I have to accomplish.

1) Down load micro-code and stuff like that when ever a user pushes a button.

2) Deterministically transmit a small command packet that sets some control parameters.

I will never have to do both operations at the same time.

I would like to do task 1) in a windows environment.
I have to do task 2) using LV-Real Time.

The windows machine will be in full control of the RT system, so I will be able to dictate that the two operations never happen at
the same time.

So...
A) Is this hardware config "legal"?

B) Is ther any thing special I have to do (like got into tri-state mode)?

C) Does any one have examples or hints that would help me get through this project with a minimum of blood loss?

Thanks for reading this,

Ben

[Chris_Rake]

It sounds like your hardware configuration is legal. Full-duplex is the same as four-wire mode, which is supported under LVRT. You'll also have to somehow associate a "button press" with the software download... if it is a virtual (on screen) button this is very easily. Otherwise you'll have to incorporate some sort of DIO circuit.

As far as tri-state goes, you should only have to do this if you ever want to disconnect the transmitter and/or receivers from the RS-485 network. Since you're operating in full-duplex mode, you probably won't have to worry about this.

My suggestion is to use NI-VISA for communication over LVRT. Then you'll need to program your routines for the command packet and for whenever the user presses the button. If you hav
e any specific tasks, feel free to post them and we can take a look at them.

Have fun!