Technical data

Advanced Triggering, Search & Navigation, and Segmented Acquisition Labs 3
4000 X-Series Oscilloscopes Advanced Training Guide 67
presented in an eye-diagram format. When clocking data into a memory
device, if the data signal is going to change polarity (high-to-low or
low- to- high), then it must switch polarities a minimum amount of time
before the occurrence of the clocking signal. This is commonly referred to
as the device’s minimum specified “setup” time. And then the data signal
must remain stable (“hold” high or low) for a minimum amount of time
after the occurrence of the clocking signal before switching to the opposite
polarity. This is commonly referred to as the device’s minimum specified
“hold” time.
Let’s assume that data is being clocked into a device on the rising edge of
our clock signal (yellow trace). To determine the setup time of our signals
we could use the scope’s timing cursors to measure the time from the
rising/falling edges of the data signal to the rising edge of the clock signal.
If you make this measurement based on the brighter green traces, then
you should measure a setup time in the range of 37 ns. But notice the
fainter green traces. It appears that our data signal is occasionally shifting
closer to the clock signal. If you make the setup time measurement based
on the fainter green traces you should measure a setup time in the range
of just 17 ns. Let’s now assume that our device has a minimum specified
setup time of 25 ns. This would mean that the timing of our signals
usually meet specification, but sometimes they are in violation of the
specification. Rather than triggering on any rising edge of the clock
(current trigger condition), triggering on clock signals that are preceded by
a data setup time violation might help us to debug this timing problem.
Let’s do it.
7 Press the [Trigger] front panel key.
8 Select the Setup & Hold trigger type.
9 Double- tap the < Setup softkey and enter 25 ns.