Best techniques for run-time communications with the PXI-8176?

[Rich Beck]

In our application, we will have a non-RT LabView GUI running on the host PC which will send messages to the RT program running on the PXI. The PXI will manage the low-level messaging over a multi-drop RS-485 line. The commands are fairly short (52 bytes or less), but the responses can contain over half a MB of data. Command files will be sent from the host PC to the PXI before messaging starts, but the data stream from the response message will have to be transferred from the PXI back to the host during RT operation. I have three questions:

1. can the TCP-IP VI's be used with the PXI?

2. if so, can we expect to keep the RT cycle going at the same time?

3. Since you say the shared memory VI's aren't
needed with the PXI, is it possible to use shared memory between the host PC and the PXI?

4. If shared memory isn't available for the PC <-> PXI communications we had in mind, are there techniques for communication that won't disturb the RT cycle of the PXI?

--Rich Beck

[JeffBoettcher]

Hello Rich,

Let's jump right into the answers:
1. Yes.
2. Yes, see details below.
3. No, the shared memory VIs can only be used to communicate between a PCI/PXI 7030-based device and the Windows computer it is install in.
4. Yes, see details below.

As you elude to, TCP communication is not deterministic, and should not be done within your time critical loop. However, there are deterministic ways to get data from your time-critical loop to a normal priority VI running on the RT engine, which can then in turn send data via TCP without interfering with your time-critical code.

The link below points to a section of the NI Developer Zone that deals with these types of issues. The document of particular interest is entitled, "TCP/IP between the Host PC and Re
al-Time Series Hardware".

Communicating with a Real-Time Engine