DocID017063 Rev 5

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AN3154

CAN settings

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Next, the code initializes the serial interface accordingly. Using this calculated baud rate, an

acknowledge byte (0x79) is returned to the host, which signals that the STM32 is ready to

receive commands.

2

CAN settings

The STM32 CAN is compliant with the 2.0A and B (active) specifications with a bitrate up to

1 Mbit/s. It can receive and transmit standard frames with 11-bit identifiers as well as

extended frames with 29-bit identifiers.

Figure 3 shows a CAN frame that uses the standard identifier only.

Figure 3. CAN frame

In this application, the CAN settings are:

•

Standard identifier (not extended)

•

Bitrate: at the beginning it is 125 kbps; during runtime it can be changed via the speed

command to achieve a maximum bit rate of 1 Mbps.

The transmit settings (from the STM32 to the host) are:

•

Tx mailbox0: On

•

Tx mailbox1 and Tx mailbox2: Off

•

Tx identifier: (0x00, 0x01, 0x02, v03, 0x11, 0x21, 0x31, 0x43, 0x63, 0x73, 0x82, 0x92)

The receive settings (from the host to the STM32) are:

•

Synchronization byte, 0x79, is in the RX identifier and not in the data field.

•

RX identifier depends on the command (0x00, 0x01, 0x02, 0x03, 0x11, 0x21, 0x31,

0x43, 0x63, 0x73, 0x82, 0x92).

•

Error checking: If the error field (bit [6:4] in the CAN_ESR register) is different from

000b, the message is discarded and a NACK is sent to the host.

•

In FIFO overrun condition, the message is discarded and a NACK is sent to the host.

•

Incoming messages can contain from 1 to 8 data bytes.

Note:

The CAN bootloader firmware supports only one node at a time. This means that CAN

Network Management is not supported by the firmware.