There are several commonly used trigger modes for oscilloscopes.
For digital oscilloscopes, the entire machine works under the control of the trigger circuit. The trigger circuit determines when the oscilloscope acquires the signal and when it stops to display the waveform. The trigger mode indicates the working status of the oscilloscope before and after the trigger conditions are met. Commonly used trigger modes for oscilloscopes include the following:
AutoTrigger Mode: This is the default trigger mode of most oscilloscopes. In the automatic trigger mode, the oscilloscope will give priority to detecting whether the set trigger conditions are met. If the trigger conditions are met, the oscilloscope will trigger according to the current trigger conditions; if the trigger conditions are not met and last for more than a certain time (usually tens of ms), the oscilloscope will automatically generate a trigger internally and capture the waveform display. If the oscilloscope automatically triggers, the captured waveform may not meet the trigger conditions. However, this avoids the situation where the user cannot see the signal waveform at all due to incorrect trigger condition settings. The user can automatically trigger the captured waveform based on the oscilloscope. The waveform can be further changed or the triggering conditions can be optimized. The automatic trigger mode can be applied to most testing situations, but it also has certain restrictions. If the signal transition that the user is interested in or the set trigger condition occurs very rarely, for example, it only occurs once per second, then if the oscilloscope is working in the automatic trigger mode, it may not have time to wait for the signal that meets the trigger condition. The oscilloscope automatically triggers, resulting in a situation where the captured signal is not the expected signal. In the automatic trigger mode, whether it is a trigger that meets the conditions or a trigger automatically generated by the oscilloscope, once triggered, the oscilloscope will process and display the captured waveform, and then wait for the next trigger to arrive. Therefore, no matter whether the trigger conditions are met or not, the oscilloscope will display the captured waveform. The waveforms are all "moving".
Normal trigger (NormalTrigger Mode): If the signal that the user wants to capture occurs at a long interval and the trigger conditions are set correctly, the oscilloscope can be set to the normal trigger mode. In normal trigger mode, the oscilloscope will trigger strictly according to the set trigger conditions. If the trigger conditions are not met, the oscilloscope will wait for the arrival of a signal that meets the trigger conditions and will not trigger automatically. In the normal trigger mode, once triggered, the oscilloscope will process and display the captured waveform, and then wait for the arrival of the next trigger. Therefore, if a waveform with trigger conditions continues to arrive, the waveform on the oscilloscope will "move"; if a waveform that meets the trigger signal never arrives, the waveform on the oscilloscope will not move or be updated.
Single trigger (SingleTrigger Mode): Under normal trigger conditions, when a new waveform that meets the trigger conditions arrives, the previous waveform will be updated, and sometimes it is necessary to capture some single or transient situations (such as capturing The waveform when the system is powered on, the waveform when the switch is turned on, the waveform when the clock just starts oscillating, etc.), we are concerned about the waveform of the first signal that meets the trigger conditions. At this time, the oscilloscope can be set to single trigger mode. . In the single trigger mode, once the trigger conditions are met, the oscilloscope will process and display the captured waveform, and will no longer perform subsequent triggering and acquisition.
Although digital oscilloscopes have a relatively large dead time, due to the use of digital technology, very rich trigger conditions can be set. If the user can roughly estimate the signal characteristics that may be captured, he can set corresponding trigger conditions for capture based on the signal characteristics. It can be said that whether the trigger condition can be set according to the signal characteristics to capture the signal reflects the user's proficiency in operating the oscilloscope. In the following chapters, we will introduce in detail the meaning of trigger conditions commonly used in oscilloscopes, and how to set trigger conditions to capture signals.
