Datasheet

Application Note
www.tektronix.com/oscilloscopes14
A TDP1000 Differential Probe is used to probe a USB
extension cable between the computer and the USB memory
device. Before connecting the probe to the cable, we use the
TDP1000 menu button on the probe to AutoZero the probe’s
4.25 V range.
To define a USB bus, we go to the bus menu and select USB
from the list of supported standards. We then follow the setup
buttons from left to right to define the parameters of our bus:
speed, source channels, type of probe, and thresholds. The
full-speed preset 1.4 V and -1.4 V thresholds are used in this
example.
First, we can check the enumeration process by triggering on
the SETUP token. After enumeration, we can verify the Start
of Frame (SOF) packets by triggering on them and verifying
the speed by checking if the J idle state is positive or by
measuring the bit width of the SOF SYNC field.
Next, we can configure the oscilloscope to trigger on a NAK
token and then put the oscilloscope in Single acquisition
mode. We then have the computer request data from the
memory device. If the memory device is ready to transfer data,
the oscilloscope will not trigger. But, if the memory device is
not ready to transfer data, it will send a NAK in response to
the computer host IN token and the oscilloscope will trigger
on the NAK. Figure 22 shows the NAK acquisition.
Working with USB 2.0
USB serial triggering and analysis support is available on
select Tektronix oscilloscopes (see Appendix A). For low-
speed and full-speed USB, trigger, decode and search
support is provided by all of the oscilloscope models. For
high-speed USB, a ≥1 GHz oscilloscope model is required.
As an example, the data latency performance of a full-speed
memory device is checked by seeing if the memory device
responds with NAK to the computer IN token request for data
from the memory device.
Figure 22. Full-speed memory device responded with a NAK to the host first IN token
request at cursor A.