Why Do I Get Errors When Making a Connection on the NI PXIe-2790?

Updated Feb 27, 2019

Reported In


  • PXIe-2790


  • LabVIEW
  • NI-DAQmx 18.5

Issue Details

I am trying to make a connection on the NI PXIe-2790 and received one of the following errors:
  • -29033, -200179, or -1074126836
When you call Connect between SUMAB and COMA and/or COMB an error is thrown informing you that the connection is already made.
  • -200200, or -1074126845
When you call Connect from COMA or COMB to another channel an error is thrown informing you that the COMA and/or COMB channels are already in use in another connection.

Why am I receiving these errors and how do I correct these issues?


The errors that you are receiving are likely caused by the fact that you have not disconnected the SUMAB channel from the COMA and COMB channels.
The solution is to disconnect the connections in software before attempting to make the new connections. See figures 1, 2 and 3 for information on how to disconnect signals in NI-SWITCH, NI-DAQmx, and NI Switch Executive.

Figure 1: How to Disconnect in NI-SWITCH

Figure 2: How to Disconnect in NI-DAQmx
Figure 3: How to Disconnect in NI Switch Executive

Additional Information

The NI PXIe-2790 module is a RF Mux made up of separate SPDT relays. Because of this, the NI PXIe-2790 is always physically connected to some path, regardless of the software state of the switch.

When the device is reset, or the Disconnect All command is made, the switch is set to the initial connection path of the device. This initial connection is from COMA to SUMAB, and COMB to SUMAB.

Since there is physically a path connected at the time that the reset or Disconnect All command is given, the driver calls a Connect command immediately following the execution of the reset or Disconnect All commands. This allows the hardware state, and the software state of the channel connections to always be identical. This was established to prevent users from incorrectly assuming that there are no signals connected, potentially causing damage.

Note: The new connection style was implemented in NI-DAQmx 9.6.1 and/or NI-SWITCH 4.6.1. Use of the NI PXIe-2790 in earlier versions of the driver would not have the Connect function called after a reset and/or Disconnect All.


Not Helpful