1. Field of Invention
The present invention pertains to the field of measurement and control systems. More particularly, this invention relates to distributed trigger nodes in measurement and control systems.
2. Art Background
A measurement and control system typically includes a set of measurement and control devices. One example of a measurement and control system is a test system which includes a set of instruments which are arranged to provide stimuli to and/or measure responses of a system or device under test. Examples of instruments include volt meters, oscilloscopes, signal generators, and logic analyzers to name a few examples.
It is often desirable in a measurement and control system to provide relatively precise timing of the activities performed by the measurement and control devices. Such precision may involve a single measurement and control device or multiple measurement and control devices. For example, it may be desirable to cause a signal generator to apply a particular signal at a particular time or cause an oscilloscope to measure a response to the particular signal at a particular time.
One prior method for coordinating the activities of measurement and control devices involves the use of an instrument control bus. An example of an instrument control bus is one that conforms to the IEEE 488 standard. For example, the application of stimuli and/or the measurement of responses by instruments may be triggered by transferring a xe2x80x9cgroup execute triggerxe2x80x9d command to the instruments via the control bus. Unfortunately, the time interval between receipt of a group execute trigger command by an instrument and the actual application of stimuli or measurement of a response by that instrument typically varies from instrument to instrument. This variation in instrument timing may be unsuitable for measurement and control systems which require more precise coordination among the instruments.
Another prior method for coordinating the activities of measurement and control devices involves precisely controlling the timing of analog trigger signals applied to the trigger inputs of the measurement and control devices. For example, an instrument typically provides one or more trigger inputs for controlling the timing of its stimulus or measurement function. Unfortunately, the adaptation of analog signaling to a measurement and control system is usually time consuming. This typically increases the costs of a measurement and control system. Moreover, changes to a measurement and control system such as relocation of instruments or replacement of instruments usually require changes to the analog signaling design and thereby increases costs associated with a measurement and control system.
A trigger node for a measurement and control system is disclosed which enables relatively precise timing in the application of stimuli and/or measurement of responses without specialized adaptation of analog signaling to the measurement and control system. A trigger node according to the present teachings includes a synchronized clock that maintains a time using a synchronization scheme that provides the timing precision needed for the application of stimuli and/or measurement of responses. A trigger node according to the present teachings further includes mechanisms for asserting a trigger signal when the time from its synchronized clock matches a trigger time associated with the trigger signal. Multiple trigger nodes may be used to coordinate the timing of multiple measurement and control devices by appropriately setting the trigger times in the trigger nodes.
Other features and advantages of the present invention will be apparent from the detailed description that follows.