wiring and using a 2-wire RS-485 serial port.

[bmihura]

I read the following on one if NI's links:

In 2-wire transmission (half- duplex), TXD+ and RXD+ on the master are wired together to TXD+ and RXD+ on the slave(s). TXD- and RXD- on the master are wired together to TXD- and RXD- on the slave(s).

Does this mean they're wired internally on the NI product, or do I have to wire "TXD+ and RXD+" then "TXD- and RXD-" together on each port?

Then to actually "use" the port, in CVI and/or MAX, do you have to configure the port as a master or slave? If so, how is this done in CVI and/or MAX?

[JoshuaP]

The NI-Serial driver does allow you to select in software which wire-mode you are using, but this does not make the actual wire connections. Setting the wire mode, just tells the driver if it needs to disable the receiver when it transmit or not. You will need to physically wire the TX+ to RX+ and the TX- to RX-.

I hope this helps.

-Josh

[bmihura]

Is the attached picture accurate?

Also, since it's "2-wire", is attaching the grounds really necessary?

[Emilie S.]

Hi bmihura:

The picture looks accurate.  Yes you do still need to connect the ground, the fact that it is two wire does not make a difference.

Regards,

Emilie S.

[bmihura]

thanks