OVMS3-idf/examples/peripherals/can/can_network/README.md

CAN Network Example

Overview

The CAN Network Example demonstrates communication between two ESP32 modules (master and slave) using the CAN2.0B protocol. CAN is a multi-master protocol, therefore the concept of master/slave in this example refers to which node initiates and stops the transfer of a stream of data messages. The example also includes an optional Listen Only module which can passively receive the CAN messages sent between the master and slave module without participating in any CAN bus activity.

The CAN Network Example will execute the following steps over multiple iterations:

1. Both master and slave go through initialization process
2. The master repeatedly sends PING messages until it receives a PING_RESP from the slave. The slave will only send a PING_RESP message when it receives a PING message from the master.
3. Once the master has received the PING_RESP from the slave, it will send a START_CMD message to the slave.
4. Upon receiving the START_CMD message, the slave will start transmitting DATA messages until the master sends a STOP_CMD. The master will send the STOP_CMD after receiving N DATA messages from the slave (N = 50 by default).
5. When the slave receives the STOP_CMD, it will confirm that it has stopped by sending a STOP_RESP message to the master.

External Transceiver and Pin Assignment

The CAN controller in the ESP32 does not contain an internal transceiver. Therefore users are responsible for providing an external transceiver compatible with the physical layer specifications of their target ISO standard (such as SN65HVD23X transceivers for ISO 11898-2 compatibility)

The CAN controller in the ESP32 represents dominant bits to the transceiver as logic low, and recessive bits as logic high. The Network Example utilizes the following default pin assignments

• TX Pin is routed to GPIO21
• RX Pin is routed to GPIO22

The following diagram illustrates an example network

    ----------   ----------   --------------  
   |  Master  | |  Slave   | | Listen Only  | 
   |          | |          | |              | 
   | 21    22 | | 21    22 | | 21    22     | 
    ----------   ----------   --------------  
     |      |     |      |     |      |   
     |      |     |      |     |      |   
    ----------   ----------   ----------  
   | D      R | | D      R | | D      R | 
   |          | |          | |          | 
   |  VP230   | |  VP230   | |  VP230   | 
   |          | |          | |          | 
   | H      L | | H      L | | H      L | 
    ----------   ----------   ----------  
     |      |     |      |     |      |   
     |      |     |      |     |      |   
  |--x------|-----x------|-----x------|--| H
            |            |            |
  |---------x------------x------------x--| L

Note

If there appears to be no activity on the CAN bus when running the example, users can try running the can_self_test example to verify if their transceivers are wired properly.