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13. CAN Transmit
In addition to the dashboard having the ability to read a CAN data stream, it can also be used to transmit
custom CAN messages. A maximum of 10 message IDs may be transmitted at individual speeds of 10, 20,
50 or 100Hz.
CAN transmit has several uses, including transmitting data from analogue sensors connected to the dash
to other devices such as the engine ECU, data loggers, on-board camera systems etc. The function may
also be used to ‘bridge’ two different physical CAN busses, even if they are operating at different speeds.
13.1 Configuring a CAN transmit channel
Click on the
CAN Transmit
tab at the top of the main window. The top half of the window contains a list of
10 unpopulated CAN channels.
Click on the small grey box at the left of the first channel to enable it, then click on the Id field to the right.
Note: The CAN Id may be entered in either decimal or hex-decimal format depending on the selection you
make under the Options menu at the top of the screen.
Working along to the right, you can then specify the bus number you wish to use, whether the message is
standard (11-bit) or extended (29 bit), the transmit frequency and the ‘Endian’ (Motorola or Intel).
To add data channels to the message frame, move to the lower half of the window and you will see a list of
8 slots representing the 8 bytes of the message frame. The top slot in the list represents the first byte of the
message. Click under the channel heading (currently set to unused) and you can then select from a pull-
down list of available channels. These channels may be transmitted as a single byte, or more commonly a
2-byte word. This is selected under the “Size” heading. If Word or Signed Word is selected then the
following byte is automatically greyed out.
Note: If a 2-byte channel is transmitted as a single byte then the least significant byte is removed. This will
result in greatly reduced resolution of the transmitted data.
Shown on the following page is a configuration used to transmit the 5 dashboard analogue channels to a
MoTeC M800 ECU using its ‘ADL receive’ function which uses ‘compound addressing’. In this case, the
first word of the message is used to transmit the first frame identifier number (0000).
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CAN Transmit page
Notes:
•
When “Constant” is selected”, you must enter an “On Value” to specify a value for the transmitted
data.
•
When “Alarm” is selected, you must enter both an “On Value” and an “Off Value”. The actual values
can be arbitrary, providing that the receiving device is configured appropriately. Conventionally we
would transmit 0 for ‘off’ and 1 for ‘on’.
