50
Subject to change without notice
S e r i a l b u s a n a l y s i s
13.3.1 I
2
C BUS Configuration
Prior to the BUS configuration it is necessary to set
the correct logic level for the digital channels (see
chapter 11.2) or the analog channels (see chapter
4.5). The default setting for both is 500 mV.
Make sure that a complete message of a serial pro-
tocol is always displayed on the screen to ensure
decoding can function properly. The Zoom function
allows you to view details for any specific message.
Fig. 13.6: Menu for the definition of I
2
C sources
To decode the I
2
C bus it is necessary to determine during the
bus configuration which
logic channel will be connected to the
clock and which one to the data line. This setting is selected
after choosing the BUS TYPE I
2
C in the BUS menu and pressing
the soft menu key
CONFIGURATION
. In the menu, choose the
top soft menu key
CLOCK SCL
and use the universal knob to
select the
source channel. You can define the data channel by
pressing the soft menu key
DATA SDA
. A small window provides
information about the current settings.
If the option HOO11 is installed, it it only possible
to select analog channels as source. If the option
HOO10 is installed, both analog and digital channels
are available as source.
Press the MENU OFF button twice to close all menus.
Fig. 13.7: I
2
C message decoded with hexadecimal values
Certain portions of the I
2
C messages will be displayed in color
to distinguish between the different elements. If the data lines
are selected with the table display, the respective sections will
also be displayed in color. These are described as follows:
Read address:
Yellow
Write address:
Magenta
Data:
Cyan
Start:
White
Stop:
White
No acknowledge:
Red
Acknowledge:
Green
The decoding of the address is performed as a 7 bit
value. The 8th bit for the write/read distinction will
be decoded in color, not in the HEX value of the ad-
dress.
13.3.2 I
2
C Bus Triggering
After the
BUS configuration, it will be possible to trigger on
various events. Press the TYPE button in the TRIGGER section of
the control panel and choose the soft menu key
SERIAL BUSES
.
Then press the SOURCE button in the TRIGGER section and
choose I
2
C Bus. This will only be available if it was configured
earlier. Press the FILTER button in the TRIGGER section of the
control panel to list all available
I
2
C
trigger conditions.
You can trigger on the
START signal (the start signal is the fall
-
ing slope on SDA when SCL is high), and the STOP signal (the
start signal is the rising slope on SDA when SCL is high) of all
messages as well as on a RESTART (the new start signal is a
repeated
start signal) or on a NOT-ACKNOWLEDGE condition.
The NOT-ACKNOWLEDGE bit is the 9th bit in a data or address
unit of the SDA line. For NOT-ACKNOWLEDGE, the Acknowledge
bit is on SDA high, although it should be low.
The soft menu key
READ/WRITE
offers additional trigger op
-
tions. You can use the soft menu key MASTER to toggle the
trigger condition between read and write access. The 8th bit of
the first data unit (depending on the address length) is used to
distinguish between read and write access. The selected condi
-
tion is displayed in the I
2
C settings window and is highlighted
by the menu key in blue.
The address length (in bit) defines the maximum number of
slave addresses to be used with the bus. For a 7 bit address
length, the maximum number of available addresses is 112.
The 10 bit addressing mode is downward compatible with the
7 bit addressing mode by using 4 of 16 reserved addresses and
Fig. 13.8: I
2
C READ/WRITE trigger menu
