How to ? Tracking down I2C serial bus anomalies
1. Connect a probe between a Ch <1–4> input of the instrument and the SCLK signal of the I
2
Cserial
bus in your system under test.
2. Connect a second probe between one of the other Ch inputs of the instrument and the SDA data
signal of the bus.
3. Push the Autoset front-panel button.
4. From the Digital menu, select Bus Setup.
5. Click Serial as the Bus Type and select I2C.
6. Click the Input box of the SCLK component and select the channel connected to the SCLK signal
in step 1.
7. Double-click the Threshold entry box, and use the keypad or the multipurpose knobs to change the
voltage reference threshold level.
8. Click the Input box of the SDA component and select the channel connected to the SDA signal in
step 2.
9. Double-click the Threshold entry box, and use the keypad or the multipurpose knobs to change the
level.
10. Click the Config tab and set the bus display parameters. The instrument ac quire s, decodes and displays
data from the bus customized for you to more readily interpret and analyze activity on the bus.
11. From the Trig menu, select Bus Setup.
12. Clic
k the Bus box and select the appropriate Bus setup <B1-B16> to acquire data from the I
2
C bus.
13. Click the Trigger On box , and select the bus cycle or activity for the instrument to use as the trigger.
For some Trigger On selections, you need to set additional fields to define other parameters such as
for an Address. In this example, you need to set an Address Format, Address Value (click the Edit
bu
tton), Data Direction, and Addressing Mode. Optionally, you can a lso set the component threshold
levels through the Logic Thresholds Setup button.
14
.
Ac
quire data and analyze the physical layer. If an analog channel is displayed, you can use Cursors to
take manual measurements or you can take automatic measurements.
1
5.
P
ush the MultiView Zoom button and scroll to see all the events. Do you have all the packets that you
expected to have? If not, at least you have narrowed your search down to the last packet sent.
16. Analyze the decoded packets in the protocol layer. Did your program send the data bytes in the
correct order? Did you use the correct address?
DSA/DPO70000D, MSO/DPO/DSA70000C, DPO7000C, and MSO/DPO5000 Series 591
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