Technical data

74 3000 X-Series Oscilloscopes Advanced Training Guide

4 Serial Bus Decoding & Triggering, Search & Navigation, and Segmented Acquisition Labs

Your scope should now be decoding I

C serial bus traffic as shown in

Figure 51. We can see automatic decoding of this I

C bus in two formats.

The blue trace at the bottom of the display shows time- aligned decoding of

the serial bus traffic, while the lister table at the top of the display shows

C decoding in a tabular format.

C addresses can be decoded in either an 8- bit or 7- bit format. The MSB

of an 8-bit address byte is the READ/WRITE bit, while the lower seven

bits define the address. The scope already detects the MSB of the address

byte and symbolically decodes it as to whether the address byte is a Read

or Write instruction. So the typical address decoding format most

engineers prefer is the 7- bit format, which is what we have selected. But

you also have the option of seeing the address byte in an 8- bit format,

which will include the MSB Read/Write bit.

Note that your scope should still be triggering on random edge crossings of

channel- 1. Let’s now set up the scope to trigger when it detects a Read

operation from address = 29

HEX

, following by an “acknowledge”, followed

by any data content (don’t care).

18 Press the [Trigger] front panel key; then select Serial 1 (I

C) using the

Entry knob.

19 Press the Trigger: Start softkey; then select Frame(Start:Addr 7:Read:Ack:Data)

using the Entry knob.

20 Press the Address softkey; then set to 0x29 using the Entry knob.

Figure 51 Decoding I

C serial bus traffic.