Debugging the Controller Area Network (CAN) buses used in today’s automotive
systems usually requires investigating both the logical and physical layers. Dedicated
CAN bus analyzers exist for debugging at the logical level, but the oscilloscope is the
primary measurement tool for testing and debugging the physical layer. The electrical
environment in automobiles is naturally harsh with lots of noise and often unexpected
transients. The core competence of an oscilloscope is its ability to capture and
display details of the noise and infrequent transients that could be producing CAN bus
errors.
Using a scope to capture data on the CAN bus
To assist in synchronizing on and identifying specific CAN frames (packets of data),
most of today’s mid-range and higherperformance oscilloscopes have the ability
to trigger on and decode the CAN bus in a hexadecimal and/or binary format
In this example, the oscilloscope has been set up to trigger on frame ID 0x201(HEX).
In addition to decoding the frame ID, the oscilloscope also decoded the 8-byte
data field as “0B A8 00 00 27 10 00 00.” The measurement capture is successful,
but it leaves the engineer with the task of abstracting the result to a result that is
meaningful within the context of the application.
Elevating the conversation to humanspeak with CAN-dbc
The new CAN-dbc symbolic trigger and decode capability in Agilent InfiniiVision 4000
X-Series scopes offer the best of both approaches: the high-level symbolic perspective
of a dedicated CAN bus debugger and the physical layer investigation capabilities
of a high-performance oscilloscope
shows the same measurement but now triggering on and decoding the
CAN bus symbolically using the enhanced CAN-dbc symbolic trigger and decode
capability. Instead of attempting to manually interpret cryptic hexadecimal codes,
the oscilloscope symbolically decodes it in “human language.”
In this example, the oscilloscope is decoding a message named “Brake_Torque.”
In addition, the oscilloscope translates raw bits into signed variables with units
as well as encoded states. For instance, Total_Torque = 131.064 kft-lbs, as opposed
to 0B A8.
In order for the oscilloscope to decode the CAN bus symbolically, you’ll need to import
that particular vehicle’s .dbc file (“data base CAN”) into the scope. All automotive
makers have created .dbc files for their vehicles’ CAN buses. However, these files are
proprietary and top secret, so if you don’t have access to one, you’ll need to create it.
The most common tool used today is Vector Informatik GmbH’s CANdb++ software.
Once the .dbc has been imported into the oscilloscope, you have the option of triggering
on and decoding the bus in low-level hexadecimal format, high-level symbolic
format, or both. This makes testing and debugging the CAN bus quicker and more
intuitive.
systems usually requires investigating both the logical and physical layers. Dedicated
CAN bus analyzers exist for debugging at the logical level, but the oscilloscope is the
primary measurement tool for testing and debugging the physical layer. The electrical
environment in automobiles is naturally harsh with lots of noise and often unexpected
transients. The core competence of an oscilloscope is its ability to capture and
display details of the noise and infrequent transients that could be producing CAN bus
errors.
Using a scope to capture data on the CAN bus
To assist in synchronizing on and identifying specific CAN frames (packets of data),
most of today’s mid-range and higherperformance oscilloscopes have the ability
to trigger on and decode the CAN bus in a hexadecimal and/or binary format
In this example, the oscilloscope has been set up to trigger on frame ID 0x201(HEX).
In addition to decoding the frame ID, the oscilloscope also decoded the 8-byte
data field as “0B A8 00 00 27 10 00 00.” The measurement capture is successful,
but it leaves the engineer with the task of abstracting the result to a result that is
meaningful within the context of the application.
Elevating the conversation to humanspeak with CAN-dbc
The new CAN-dbc symbolic trigger and decode capability in Agilent InfiniiVision 4000
X-Series scopes offer the best of both approaches: the high-level symbolic perspective
of a dedicated CAN bus debugger and the physical layer investigation capabilities
of a high-performance oscilloscope
shows the same measurement but now triggering on and decoding the
CAN bus symbolically using the enhanced CAN-dbc symbolic trigger and decode
capability. Instead of attempting to manually interpret cryptic hexadecimal codes,
the oscilloscope symbolically decodes it in “human language.”
In this example, the oscilloscope is decoding a message named “Brake_Torque.”
In addition, the oscilloscope translates raw bits into signed variables with units
as well as encoded states. For instance, Total_Torque = 131.064 kft-lbs, as opposed
to 0B A8.
In order for the oscilloscope to decode the CAN bus symbolically, you’ll need to import
that particular vehicle’s .dbc file (“data base CAN”) into the scope. All automotive
makers have created .dbc files for their vehicles’ CAN buses. However, these files are
proprietary and top secret, so if you don’t have access to one, you’ll need to create it.
The most common tool used today is Vector Informatik GmbH’s CANdb++ software.
Once the .dbc has been imported into the oscilloscope, you have the option of triggering
on and decoding the bus in low-level hexadecimal format, high-level symbolic
format, or both. This makes testing and debugging the CAN bus quicker and more
intuitive.