Plexim PLECS RT Box User manual

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RT Box
DEMO MODEL
CAN channel loop-back demo on a single RT Box
Last updated in RT Box Target Support Package 2.0.5

CAN channel loop-back demo on a single RT Box
1 Overview
A Controller Area Network (CAN bus) is a robust vehicle bus standard designed to allow microcon-
trollers and devices to communicate with each without a central host computer. A CAN connector is
available on RT Box 2 and 3 and hardware revision 1.2 of the RT Box 1. The connector drawing and
pin-out can be found in the CAN interface section of the RT Box User Manual. There are two CAN
channels available on the connector, each having a pair of High (CAN_H) and Low (CAN_L) signals.
This demo model shows:
• a simple loop-back scenario that connects the two CAN channels,
• how to use data base CAN (.dbc) files to configure the CAN Pack and Unpack blocks,
• how to use the valid port of the Can Receive block to trigger a calculation upon arrival of new data.
1.1 Requirements
To run this demo model, the following items are needed (see www.plexim.com):
• One PLECS RT Box and one PLECS Coder license. For the RT Box 1 the minimum hardware revi-
sion is 1.2.
• The RT Box Target Support Library
• Follow the step-by-step instructions on configuring PLECS and the RT Box in the Quick Start guide
of the RT Box User Manual.
• Wires to connect the CAN_H pin of channel 1 and 2, and CAN_L pin of channel 1 and 2 together.
See Fig. 1 for an illustration.
15
6 9
Figure 1: Loop-back wiring of CAN channel 1 and 2 on the rear panel of the RT Box
2 Model
This demo model shows the CAN transmitting and receiving functions on two different channels in-
side the same subsystem. With the wiring setup shown in Fig. 1, a loop-back of the CAN message be-
tween two channels is formed. The circuit schematic is shown in Fig 2. The CAN Pack block generates
a CAN message with PLECS signals as its inputs. Next, it interfaces with the CAN Transmit block to
send out the CAN message. On the receiver side, after the CAN Receive block a CAN Unpack block is
used to unpack the CAN message into PLECS signals that are displayed in a scope.
CANPack
id
data
Test_uint
Test_digital
Test_int
Test_float
10
CANTransmit
interface:
CAN2
d
id
CAN
TX
Processed
Data
CANReceive
interface:
CAN1
d
v
CAN
RX
f:
1/Ts_trans
DataProcessing
(atarrivalofnewdata)
data
Result1
Result2
RX
round
TX
RX
v
v
Figure 2: Subsystem circuit schematic for CAN loop-back demo
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CAN channel loop-back demo on a single RT Box
Note The CAN Pack block forces data type casting on the signals feeding into it. Data type inconsis-
tencies between the “Output data type” of the feeding signals and the signal data type defined inside the
CAN Pack block should therefore be avoided.
2.1 CAN Transmitting
The CAN Pack block generates a CAN message by packing the input signals into a byte vector (see
. Fig. 3). The CAN ID field specifies the ID of the CAN message. In this demo, it is set as 0x1. The
CAN ID can be supplied as either an 11-bit value (for CAN 2.0A compliance) or 29-bit value (for CAN
2.0B compliance). The id terminal of the block must be connected to the id terminal of the CAN
Transmit block to use this parameter in the generated CAN message. A signal in a CAN message is
defined by its data type, its byte order (Little Endian / Big Endian) and its start bit and length within
the 64-bit CAN message. A signal can be scaled and an offset can be applied to efficiently send float-
ing point signals as integers. The bits within the CAN message are numbered from 0 (least significant
bit of the first byte) to 63 (most significant bit of the last byte). The signal definitions can optionally
Figure 3: Mask content of the CAN Pack block
be imported from a DBC (data base CAN) file by clicking the Import DBC ... button. Then browse to
the can_loopback.dbc file provided with this demo model and click Open. One should see the same
CAN message signal definitions as originally listed in CAN Pack block. Clicking Import will finish the
import DBC process.
Most CAN networks are proprietary in the sense that only the Original Equipment Manufacturer
(OEM) has the DBC file required to decode the data. This is the case, for example for raw CAN data
in most cars, bikes, EVs, production machinery, etc.
In this demo model, we send out:
1an unsigned integer type from bit 0 to bit 14 (15-bit length) provided by a Constant block,
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CAN channel loop-back demo on a single RT Box
2abool type digital signal on bit 15 provided by a Pulse Signal of 1 Hz and 0.5 duty cycle with val-
ues alternating between 0 and 1,
3a 5 Hz Triangular Wave between -5 and +5 as a signed integer type from bit 16 to bit 31 (16-bit
length),
4a 5 Hz Sine Wave with amplitude of 1 as a float type from bit 32 to bit 63 (32-bit length).
This information is stored in a total of 64 bits which corresponds to the maximum amount of data in
one package. Note that the Constant block for the first test signal is added into the Exceptions field
of the Parameter Inlining tab of Coder options... window. This means that once the model is run-
ning in real-time, the value can be tuned during a real-time simulation in the External Mode.
Figure 4: Mask content of the CAN Transmit block
The CAN Transmit block sends out a message on the CAN bus. Fig. 4 shows the mask content of the
CAN Transmit block.
• CAN channel 2 is used as the transmitter channel and is therefore chosen under CAN interface
field.
• The CAN ID source field is chosen as External because it is provided from the CAN Pack block as
an input signal. One can also choose the ID source as a Parameter and specify the CAN ID here.
• The Execution field can be chosen as regular or triggered. If regular is chosen, in the next field,
Sample time, one can specify the time period for regular packet transmission. This demo uses a
triggered execution with rising trigger sensitivity. A Trigger Port is shown at the mask level of
the CAN Transmit block to which a Pulse Generator is connected with frequency equal to the CAN
transmission sample time (0.01 Seconds).
• The Offline simulation field enables or disables the Target Inports on the root schematic that al-
low the simulation of CAN Messages in an offline simulation.
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CAN channel loop-back demo on a single RT Box
2.2 CAN Receiving
The CAN Receive block receives a CAN message. On reception of a CAN message the data is made
available on the block output das a vectorized signal consisting of 8 bytes. The output vis 1 in each
simulation step where new (and valid) data is received, and 0 otherwise. Fig. 5 shows the mask con-
tent of the CAN Receive block.
Figure 5: Mask content of the CAN Receive block
• CAN channel 1 is the receiver channel and set in the CAN interface parameter field of the CAN
receive block.
• Note that the CAN Transmit and CAN Receive blocks have to use the same CAN ID to realize the
loop-back of data.
• Setting the Frame format to Auto means that it uses the Base format if the specified CAN ID is
smaller than 2047. Otherwise, the Extended format is used.
• The Offline simulation field enables or disables the Target Inports on the root schematic that al-
low the simulation of CAN Messages in an offline simulation.
The CAN Unpack block decodes signals from a byte vector received over CAN into the original mes-
sage. Its CAN ID and signal definitions should be set in the exact same way as the CAN Pack block
shown in Fig. 3. One can do it by manually editing the content of CAN Unpack block or simply by se-
lecting Import DBC ... and specifying the same DBC file as is used on the CAN Pack side.
3 Simulation
The selected CAN interface must be enabled and configured in the RT Box Coder Options Dialog.
From the System tab of the Coder options... window, select the “Subsystem” and go to the Target
tab. Under the subtab CAN, make sure to check both Enable CAN1 and Enable CAN2.
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CAN channel loop-back demo on a single RT Box
•CAN1 baud rate specifies the baud rate for CAN transmission. Note that all devices on a CAN
bus must be configured to use the same baud rate. Here in this demo the default value of 500 kHz
is used.
•CAN1 tx/rx pin specifies which I/Os to use for CAN communication. The option Internal CAN in-
terface is available on all RT Box versions except RT Box 1 with hardware revision earlier than
1.2. For older revisions the digital in and out pins 26/27 can be used to set up a CAN interface.
Please note that an external CAN transceiver chip needs to be added by the user.
• If the Internal CAN interface is chosen above, a new field Termination for CAN1 will appear.
Each end of a CAN Bus should have a termination resistance of 120 Ωbetween CAN-Hi and CAN-
Low. As this example discusses a direct point-to-point connection, the termination resistance should
be enabled for both CAN interfaces.
Build the “RT Box” model onto the RT Box. Once the model is uploaded, from the External Mode
tab of the Coder options... window, Connect to the RT Box and Activate autotriggering. The real-
time simulation results are shown in Fig. 6.
• The first signal received in an unsigned integer with a value of 10. By changing the Constant value
in front of the CAN Pack block to another value (for example: from 10 to 20) during run-time, one
should see the change reflected on the first received signal of the Scope in Fig. 6 immediately.
• The second received signal is a 1 Hz, 0.5 duty cycle digital pulse alternating between 0 and 1.
• The third signal is a 5 Hz Triangular waveform with duty cycle of 0.5 changing between -5 and +5.
• The fourth signal is a 5 Hz Sine waveform with amplitude of 1.
• The fifth signal shows the valid flag asserted when new valid data arrives
One can also see in the last two signals that the 10 ms staircase effect of quantization correctly reflects
the Sample time setting in the CAN Transmit block. The “v” port signal of the CAN Receive block
goes high only when new data arrived. The signal can be used to trigger potentially time consuming
calculations implemented in a triggered/enabled subsystem. This demonstration uses a simple setup
where the first two signals are added and the last two signals are multiplied.
4 Conclusion
This RT Box demo model demonstrates a loop-back test using the integrated CAN interface on the
RT Box. It shows how to set up the CAN interface in the Coder settings and how CAN messages are
formed in a PLECS model using CAN Pack and Unpack blocks. The demo model runs in both offline
and in real-time simulation.
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CAN channel loop-back demo on a single RT Box
unit
digital
int
float
validflag
9
10
11
0.0
0.5
1.0
-5
0
5
-1
0
1
0.00 0.05 0.10 0.15 0.20
0.0
0.5
1.0
Reference
Receivedvalue
Reference
Receivedvalue
Reference
Receivedvalue
Reference
Receivedvalue
CANreceive
Figure 6: Real-time waveform showing the four received signals after CAN loop-back test
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Revision History:
RT Box Target Support Package 2.0.5 First release
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RT Box Demo Model
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