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Triggering the Oscilloscope
To use I2C triggering
3 Connect an oscilloscope channel to the SDA (serial data) line in the
circuit under test, then set the
SDA data channel softkey to that channel.
As you press the SDA softkey (or rotate the Entry knob on mixed-signal
oscilloscopes), the SDA 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
"I
2
C".
Adjust the trigger level for the selected analog channel by turning the Trigger
Level knob. For the mixed-signal oscilloscope, select Threshold in the D7 Thru
D0 or D15 Thru D8 menu to set the level for digital channels assigned to the clock
and data lines. The value of the trigger level or digital threshold is displayed in
the upper-right corner of the display.
Data needs to be stable during the whole high clock cycle or it will be interpreted
as a start or stop condition (data transitioning while the clock is high).
4Press the Trigger: softkey to select one of the following I
2
C trigger
conditions:
Start Condition: the oscilloscope triggers when SDA data transitions from high
to low while the SCL clock is high. For triggering purposes (including frame
triggers), a restart is treated as a start condition.
Stop Condition: the oscilloscope triggers when data (SDA) transitions from low
to high while the clock (SCL) is high.
Missing Acknowledge: the oscilloscope triggers when SDA data is high during
any Ack SCL clock bit.
Restart: the oscilloscope triggers when another start condition occurs before a
stop condition.
SDA
SCL
Start
Condition
Stop
Condition
Address
Ack Data
AckR/W