API Support for Switch Modules

Switch modules can support any of four different ways to control their relays. You may use the APIs interchangeably, but NI recommends using a single API for each application.

Digital Output—Create your tasks, either programmatically with the Create Channel Digital Output function/VI or interactively through the DAQ Assistant, using the digital output physical channels. Use the digital versions of the Write function/VI to control the relays. Each digital port consists of 32 digital lines, and each line represents a relay on the switch. For example, if a module contains 64 relays, the first 32 are on port 0, and the rest will be on port 1. Writing a 0 to a digital line opens the relay and writing a 1 closes it.

Immediate—The immediate API, supported by all switches, provides a switch channel-based interaction recommended for nonscanning operations. Functions/VIs such as DAQmx Switch Connect and DAQmx Switch Disconnect are considered part of the immediate API.

Relay—The relay API provides a relay-based interaction. Functions/VIs like DAQmx Switch Open Relays and DAQmx Switch Close Relays are considered part of the relay API.

Scanning—Scanning is a method of connecting channels and is often used when connecting instruments and devices under test (DUTs) in a specific order. In this operation mode, the switch cycles through each entry in a scan list downloaded to the switch. The triggers the switch receives initiate this cycling. Create scanning tasks using DAQmx Switch Create Scan List and control tasks using functions/VIs like DAQmx Start, DAQmx Stop, and so on.