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
2
C serial bus traffic as shown in
. We can see automatic decoding of this I
2
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
I
2
C decoding in a tabular format.
I
2
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
2
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
2
C serial bus traffic.