Getting Started with the MCAN (CAN FD) Module

Trademarks

C2000 and Code Composer Studio are trademarks of Texas Instruments.

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1 Introduction

CAN is a serial protocol that was originally developed for automotive applications. Due to its robustness and reliability, it now finds application in diverse areas such as industrial equipment, medical electronics, trains, aircraft, and so forth. CAN protocol features sophisticated error detection and confinement mechanisms and lends itself to simple wiring at the physical level. The original CAN protocol standard is now referred to as "classical" CAN to distinguish it from the more recent CAN FD standard. Figure 1-1 shows the typical wiring for CAN bus.

Figure 1-1 Typical CAN bus

CAN Flexible Data Rate (CAN FD) is an enhancement to the classical CAN in terms of higher bit rates and the number of bytes transferred in one frame, thus increasing the effective throughput of communication. While classical CAN supports bit rates up to 1 Mbps and a payload size of 8 bytes per frame, CAN FD supports bit-rates up to 5 Mbps and a payload size of up to 64 bytes per frame. Figure 1-2 shows the frame structure for CAN FD frames.

Figure 1-2 CAN FD Frame

1.1 MCAN Features

Salient features of the MCAN module are as follows:

Conforms with CAN Protocol (ISO 11898-1:2015)
Full CAN FD support (up to 64 data bytes)
Up to 32 dedicated transmit buffers
Configurable transmit FIFO, up to 32 elements
Configurable transmit queue, up to 32 elements
Configurable transmit Event FIFO, up to 32 elements
Up to 64 dedicated receive buffers
Two configurable receive FIFOs, up to 64 elements each
Up to 128 filter elements
Loop-back mode for self-test
ECC check for Message RAM
Clock stop and wakeup support
Timestamp counter

2 Useful tips to run the C2000ware examples

On devices like TMS320F2838xD and TMS320F2838xS, the MCAN module may be controlled either by CPU1 (28x) or the Connectivity Manager ( M4). This is not applicable for devices with only a 28x CPU. Below are some useful tips for a successful run of the examples:

For TMS320F2838xD and TMS320F2838xS devices, there may be two versions of some examples, a version that runs on CPU1 (28x) and another that runs on CM (M4). For example, in C2000ware version 3.04, CPU1 examples reside in C:\ti\c2000\C2000Ware_3_04_00_00\driverlib\f2838x\examples\c28x\mcan and the CM examples reside in C:\ti\c2000\C2000Ware_3_04_00_00\driverlib\f2838x\examples\cm\mcan. The projects have the same name, so they cannot exist together in the same CCS workspace. Before running any code on the M4 processor, the file cm_common_config_c28x.c should first be executed.
For the examples to run successfully, it is very important to ensure the clock settings are correct. This is based on the input clock to the device. For details, see below note in the device.c file.

"By default, the Device_init function assumes 25 MHz XTAL. If a 20 MHz crystal is used, add a predefined symbol "USE_20MHZ_XTAL" in your CCS project. If a different XTAL is used, please update the DEVICE_SETCLOCK_CFG macro accordingly. For example, if you are running the examples on a board with a 20 MHz input clock to the MCU, make sure USE_20MHZ_XTAL is added to the predefined symbols". For details, see Figure 2-1.

Figure 2-1 Adding the Predefined Symbol in Project Properties

If you convert a RAM-based example to a Flash based example, it is important to once again add the USE_20MHZ_XTAL symbol for the flash-based project as well.

GPIO configuration: Considering the MCAN signals can be routed to multiple pins, it is important to ensure the correct options are chosen based on your board design. By default, GPIO30 and GPIO31 are chosen for the MCAN function. The following settings are in the device.h file :

#define DEVICE_GPIO_CFG_MCANRXA    GPIO_30_MCAN_RX  // "pinConfig" for MCAN RX
#define DEVICE_GPIO_CFG_MCANTXA    GPIO_31_MCAN_TX  // "pinConfig" for MCAN TX

GPIO_30_MCAN_RX & GPIO_31_MCAN_TX are defined in pin_map.h

It is possible to communicate between MCAN and eCAN or DCAN, if FDF and BRS bits are disabled. In this case, only classic CAN frames can be used.