The ZDS2022 oscilloscope technical exchange conference is still in full swing. Recently, a customer communicated with our FAE, stating that he wanted to stably trigger the first bit of the UART data frame. He sequentially set “edge trigger” and “rising edge trigger” and then performed a single trigger in Simple mode. After multiple tests, the screen occasionally showed “not triggering on the first rising edge, but on subsequent rising edges.” What is going on here?
First of all, edge triggering does not specifically choose an “edge” or only recognize the first edge. Therefore, every edge that meets the trigger condition has the potential to trigger. In fact, the customer wants to achieve the function of stably triggering the first bit of the UART data frame. The ZDS2022 oscilloscope itself includes 21 types of protocol triggering functions, so there is no need to use edge triggering.
Figure 1: The screen shows a situation where it does not trigger on the first edge.
How to operate? We press the Trigger key, set the trigger mode to normal trigger, set the trigger type to UART, and set the protocol parameter to start bit trigger. Then press the Horiz key, setting the memory depth to 112Mpts. The large memory depth mode allows for more complete protocol decoding information at larger time bases.
Figure 2: Setting the UART protocol triggering method.
Then press the Decode key, set the decoding type to UART, and enable protocol triggering. At this point, the protocol will trigger according to the conditions set in the Trigger menu. By increasing the time base, we can see that the trigger point is accurately positioned at the first bit of the UART data frame on the main interface.
Figure 3: Triggering on the first rising edge and decoding results.
