ZDS2022 Oscilloscope 100 Practical Videos 56: Setup/Hold Trigger

Hello everyone, what method do you usually use to detect signal timing? Today I will share with you a method of using the setup/hold trigger mode to detect signal timing.

Before the sampling clock signal arrives, the data must remain stable for a period of time, that is, ΔT1 in the figure is called the setup time; if the setup time is not long enough, the data will not be able to be transmitted stably. After the sampling clock signal arrives, the data must also remain stable for a period of time, that is, ΔT2 in the figure is called the hold time; if the hold time is not long enough, the data will also not be able to be transmitted stably.

The trigger holdoff function is specially designed for large-cycle repetitions where there are many non-repeating waveform points that meet the trigger conditions. If the holdoff function is not used, the trigger point is not fixed, which will cause unstable display. After the oscilloscope uses the trigger holdoff function, after the oscilloscope is triggered for the first time, the second trigger can only be performed after the trigger holdoff time has passed. In the figure, the holdoff time can be set to a value of >200 ns but <600 ns. After using trigger holdoff, the trigger is triggered at the same point each time, so the display can be stable.

Figure 1 Setup and hold time

In order to determine whether the setup time and hold time of data transmission meet the design requirements, we use the setup/hold trigger mode. Press the [Trigger] key, set the trigger mode to normal, set the trigger type to setup/hold, and then set the corresponding clock channel and data channel. The sampling type is divided into rising edge and falling edge. The edge here means that you can specify which clock edge to sample the data. We select the rising edge, and the data type can be selected as high level and low level. We select high level and select the next page soft key. In the trigger type here, we first select setup. The next step is to set the setup time. Set the appropriate setup time according to your needs. Rotate knob A for fine adjustment and knob B for coarse adjustment. We set it to 300us. It will trigger when the setup time is less than the set time. Find the required high and low levels through the edge of the clock.

Figure 2: Creating a trigger

This trigger ensures the high-level logic state of the data signal corresponding to the rising edge of the clock, and the location of the establishment time trigger is accurately positioned at the rising edge of the clock.

In fact, the steps to maintain a trigger are similar to those to establish a trigger. Let’s try it.