CAN (Controller Area Network)

These commands provide access to the CAN hardware available on the CGCOLORMAX2.

A CAN module supports up to 32 channels, each channel can be configured to transmit or receive data. For receiving data the CAN module writes received messages into a different FIFO buffer for each channel. One entry in a FIFO buffer is 16 bytes long (4 address bytes, 4 length bytes, 8 data bytes).

These commands allow the user to specify the number of records in each FIFO buffer and the internals keep track of the memory requirements and automatically allocates memory from the available heap. A command is provided to free the allocated memory when the CAN interface is no longer required.

Note that CAN channels are numbered from 0 to 31 and that, per the Microchip documentation, CAN channels should be configured contiguously from 0 upwards. I.e. if 5 channels are required use channels 0, 1, 2, 3 & 4; and not 1, 2, 3, 4 & 5 or 3, 5, 10, 22, 31 or any other combination.

The CAN module is first configured by placing it in configuration mode and then issuing configuration commands. When the desired configuration is set up then the CAN module is enabled. Once enabled the RX and TX commands can be used to receive and send data on the bus. Once the CAN module is finished it should be disabled and the memory associated with the FIFO buffers should be freed (for example at the end of the application)

An RX channel can either have a filter for a specific id or be configured to receive all messages. In the latter case the user can request the id of the received command and then perform processing based on the id of the command. However, on a CAN bus with moderate to high utilization, more reliable operation will be achieved by setting up multiple channels with each channel filtering for one id of interest. This is because of the relatively small buffer sizes and the relatively slow operation of the BASIC interpreter – when trying to receive all messages into one buffer the buffer overruns and data is lost. Furthermore, when a channel is being filtered for a single ID it may be appropriate to set the FIFO buffer size to just 1 record, especially if the goal is to update a single value display. This will always give you the most up-to-date data.

The examples provided were designed for (and tested on) a second generation Toyota Prius (Model years 2004 – 2009).

Throughout this overview “CAN commands” have been referred to in the plural. In fact there is only one true CAN command – the other commands are “sub-commands” from this one master. By structuring the commands this way there is less impact on the limitation for the number of top-level/master commands that MMBasic can support.

EXAMPLE ONE – Minimal example of reading one channel

EXAMPLE TWO – Example of reading all channels and displaying just one (but don’t do this!)

EXAMPLE THREE – Reading manufacturer specific PID’s on a Toyota Prius 2005.

CAN-in-Automation connector pin out.

There are several types of connectors used with CAN. Illustrated here is a standard using a 9-pin D-sub connector. This follows the CiA DS-102 pin out.