55
Subject to change without notice
S e r i a l b u s a n a l y s i s
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.
To decode the
CAN BUS it is necessary to first determine
which channel will be connected to the data line. This setting
is selected after choosing the bus type CAN in the BUS menu
and 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. 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. The option
BIT RATE
defines how many bits are
transmitted per second and allows you to select default data
rates (10 / 20 / 33.333 / 50 / 83.333 / 100 / 125 / 250 / 500 kBit/s
and 1 MBit/s) 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 (KEYPAD button).
Fig. 13.21: Setting the SAMPLE POINT during the CAN configuration
13.6.2 CAN 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 CAN. 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
CAN
trigger conditions.
The function START OF FRAME triggers on the first slope of
the SOF bit (synchronizing bit). The function END OF FRAME
triggers on the end of the frame. The soft menu FRAME offers
the following options:
– ERROR:
General frame error
– OVERLOAD:
Trigger on CAN Overload frames
– DATA:
Trigger on data frames; select the correct identifier
type via universal knob
– READ DATA:
Trigger on read frames; select the correct
identifier type via
universal knob
– DATA|READ:
Trigger on read and data frames; select the
correct identifier type via
universal knob
– ID TYPE:
Identifier type (11 bit, 29 bit or any)
Fig. 13.22: CAN data trigger menu
The soft menu ERROR identifies various errors in a frame. This
menu allows you to choose one or several error message types
as trigger condition:
STUFF BIT
Individual frame segments (e.g. frame start etc.) are coded
during the bit stuffing procedure. The transmitter automati-
cally 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.
FORM
A form error occurs if a fixed bit field contains one or several
invalid bits.
ACKNOWLEDGE
An authentication error occurs if the transmitter receives no
authentication (acknowledge).
CRC (Cyclic Redundancy Check)
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 calcu
-
lates the CRC in the same manner. A CRC error occurs if the
calculated result deviates from the received CRC sequence.
The soft menu key
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 select which individual bits within
the data are to be edited.
Select the option
STATE
to assign a logic state to each bit (High
= H = 1, Low = L = 0 or X = don’t care). The state X defines any
