54
Serial Bus Analysis
list all available CAN trigger conditions:
❙
START OF FRAME:
Triggers on the first slope of the SOF
bit (synchronizing bit).
❙
END OF FRAME:
Triggers on the end of the frame.
❙
FRAME:
The submenu offers different options, like trigger
on ERROR (general frame error), OVERLOAD (trigger on
CAN Overload frames) or DATA (trigger on data frames).
With the soft menu key READ/DATA you are able to
trigger on read and data frames. With the soft menu key
IP TYPE the identifier type (11 bit, 29 bit or any.) can be
selected.
❙
ERROR S:
Identifies various errors in a frame. This menu
allows you to choose one or several error message types
as trigger condition. Individual frame segments (e.g. frame
start etc.) are coded during the bit stuffing procedure. The
transmitter automatically adds a complimentary bit to the
bit stream if it detects 5 consecutive bits with identical
value in the bit stream to be transmitted. A “STUFF” error
occurs if the 6th identical bit level is detected in the
specified sections. A
FORM
error occurs if a fixed bit field
contains one or several invalid bits. An authentication error
occurs if the transmitter receives no authentication
(acknowledge). CAN BUS applies a complex checksum
calculation (Cyclic Redundancy Check). The transmitter
calculates the CRC and transmits the result in a CRC
sequence. The receiver calculates the CRC in the same
manner. A CRC error occurs if the calculated result
deviates from the received CRC sequence.
❙
IDENTIFIER:
Identifies the priority and the logical address
of a message. In the menu that opens you can press the
top soft menu key to select the FRAME TYPE (general
data, read data or read/write data) via universal knob. The
soft menu IDENTIFIER SETUP below allows you to specify
the length of the identifier type via soft menu key ID TYPE
and universal knob (11 bit base or 29 bits for extended
CAN frames). The soft menu key COMPARE defines the
comparison function. If the pattern includes at least one X
(don’t care), it is possible to trigger on a value equal or not
equal to the specified value. If the pattern includes only 0
or 1, it is possible to trigger on an area greater than or less
than the specified value. The PATTERN INPUT may be
binary or hexadecimal. If you choose the binary input, the
soft menu key BIT and the universal knob allow you to
13.7.1 CAN BUS Configuration
After choosing the BUS type CAN in the BUS menu the
configuration menu will open after pressing the soft menu
key CONFIGURATION. In the menu that opens you can
press the top soft menu key DATA to select the desired
channel via universal knob in the CURSOR/MENU section.
An analog or a digital channel can be connected to CAN-
High or CAN-Low. In addition, it is possible to connect a
differential probe (e.g. HZO40) to an analog channel. When
using a differential probe, select CAN High if the positive
input of the probe is connected to CAN-H and the negative
input to CAN L. If the probe is connected with reversed
polarity, you must select CAN L.
The soft menu key SAMPLE POINT allows you to specify
the exact point within the bit at which the value for the
current bit is sampled. You can select a value in percent
(25% to 90%) via universal knob or KEYPAD key in the
CURSOR/MENU section. The option BIT RATE defines
how many bits are transmitted per second and allows you
to select default data rates via universal knob. Use the soft
menu key USER to specify user-defined bit rates. You can
enter the value via universal knob or numeric input (KEY-
PAD button).
Certain portions of the UART messages will be displayed
in color to distinguish between the different elements:
❙
Weiß
:
Data length code, number of data bytes
❙
Cyan
:
Data words
❙
Magenta
:
Identifier
❙
Rot
:
Frame Error
13 .7 .2 CAN BUS Triggering
After the CAN
BUS configuration, it will be possible to trig
-
ger on various events. Press the TYPE button in the TRIG-
GER section and choose the soft menu key SERIAL BUSES.
Then press the SOURCE button in the TRIGGER section and
choose CAN. This will only be available if it was configured
earlier. Press the FILTER button in the TRIGGER section to
Prior to the
BUS configuration it is necessary to set the correct
logic level (threshold). Please refer to chapter 4.5. The default
setting is 500 mV.
Fig. 13.16: CAN
BUS configuration
Fig. 13.17: CAN BUS