can I tristate a com port in 8423 card?

[Angelantoni]

Hi all

Am using 2 PXI 8186 to send commands to some COM based devices through a single RS485, 4 wire bus, but it is not possible to send commands to the device from both the PXI's. Only if one PXI is switched off the other PXI is able to send commands, i belive this is happening because both the PXI's are trying to take control of the bus. I wanted to know if there is a way in which i can tristate one of the PXI's com port so that other PXI can send the commands on the bus.

Thanx for the reply

Arun 

[Emilie S.]

Hi Arun:

I'm a little confused as to what your hardware set up is.  Can you please describe your system a little more thoroughly?  Please tell me exactly what is connected together.  Do you have 2 PXI chassis, etc.

Thank you,

Emilie S.

[Angelantoni]

Hi Emilie

I have two 1031 PXI chassis, both the chassis have two 8423 cards (with four RS485 ports) and a PXI 8186. both the PXI have to comunicate with COM devices. the block diagram is attached along with this mail. my problem is if both the PXI's are switched on they don't communicate with the devices, only one of them can take control of the bus ata time, so i wanted to know if there is away in which i can place the com ports in 8423 cards in tristate.

Thanx for the reply

regards

Arun

[Emilie S.]

Hi Arun:

You cannot have 2 "masters" on the same network.  You should have one that is a master and the rest slaves.  There is really no way to put this in "tristate" mode.

Serial Products Support

Please note the Serial Quick Reference Guide that has a small diagram on setting up a 485 network.

Regards,

Emilie S.