Agilent Technologies 7000B Series - Page 293

I
2
C/SPI Triggering and Serial Decode 11
InfiniiVision 7000B Series Oscilloscopes User’s Guide 293
7 Press the Frame by softkey to select a framing signal that the oscilloscope
will use for determining which clock edge is the first clock edge in the
serial stream.
You can set the oscilloscope to trigger during a high chip select (CS), a
low chip select (~CS), or after a Timeout period during which the clock
signal has been idle.
• If the framing signal is set to CS (or ~CS), the first clock edge as
defined, rising or falling, seen after the CS (or ~CS) signal transitions
from low to high (or high to low) is the first clock in the serial
stream.
Chip Select — Press the CS or ~CS softkey or turn the Entry knob to
select the channel that is connected to the SPI frame line. The label
(~CS or CS) for the source channel is automatically set. The data
pattern and the clock transition must occur during the time when
the framing signal is valid. The framing signal must be valid for the
entire data pattern.
As you press the CS or ~CS softkey (or rotate the Entry knob), the
CS or ~CS label for the source channel is automatically set and the
channel you select is shown in the upper- right corner of the display
next to “SPI”. When you press the Frame by softkey, the graphic
shown on the previous page changes to show timeout selection or the
current state of the chip select signal.
• If the framing signal is set to Timeout, the oscilloscope generates it’s
own internal framing signal after it sees inactivity on the serial clock
line.
Clock Timeout — Select Clock Timeout in the Frame by softkey, then select
the Timeout softkey and turn the Entry knob to set the minimum time
that the Clock signal must be idle (not transitioning) before the
oscilloscope will search for the Data pattern on which to trigger.
When you press the Frame by softkey, the graphic shown on the
previous page changes to show timeout selection or the current state
of the chip select signal.
The Timeout value can be set anywhere from 100 ns to 10 s.
8 Set the trigger levels for the Clock, Data, and (if used) CS signals to the
middle of the signals:
• If your SPI signals are connected to analog channels, press the Clock
softkey and rotate the Trigger Level knob. Repeat for the Data, ~CS, or
CS signals.