Datasheet

www.tektronix.com/oscilloscopes 9

Debugging Serial Buses in Embedded System Designs

In the example above we used a simple SS Active trigger. The

full SPI triggering capability in Tektronix oscilloscopes include

the following types:

SS Active - triggers when the slave select line goes true for

a slave device.

Start of Frame - triggers at the start of a frame when the

clock idle time is used to deﬁne the frame timing.

MOSI - trigger on up to 16 bytes of user speciﬁed data from

the master to a slave.

MISO - trigger on up to 16 bytes of user speciﬁed data from

a slave to the master.

MOSI/MISO - trigger on up to 16 bytes of user speciﬁed

data for both master to slave and slave to master (available

only on 4000/3000/2000 Series models.

Again, these triggers allow you to isolate the particular bus

trafﬁc you’re interested in, while the decoding capability

enables you to instantly see the content of every message

transmitted over the bus in your acquisition.

Upon seeing all 0s at the end of the messages we realize

we’ve made one of the most common mistakes with SPI by

programming the bits in each 24-bit word in reverse order in

the software. A quick change in the software results in the

following acquisition and a VCO correctly locked at 2.5 GHz

as shown in Figure 13.

Figure 13. Correct synthesizer conﬁguration messages.