67 lines
3 KiB
Markdown
67 lines
3 KiB
Markdown
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# CAN Network Example
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## Overview
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The CAN Network Example demonstrates communication between two ESP32 modules (master
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and slave) using the CAN2.0B protocol. CAN is a multi-master protocol, therefore
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the concept of master/slave in this example refers to which node initiates
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and stops the transfer of a stream of data messages. The example also includes
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an optional **Listen Only module** which can passively receive the CAN messages
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sent between the master and slave module without participating in any CAN bus activity.
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The CAN Network Example will execute the following steps over multiple iterations:
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1. Both master and slave go through initialization process
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2. The master repeatedly sends **PING** messages until it receives a **PING_RESP**
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from the slave. The slave will only send a **PING_RESP** message when it receives
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a **PING** message from the master.
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3. Once the master has received the **PING_RESP** from the slave, it will send a
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**START_CMD** message to the slave.
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4. Upon receiving the **START_CMD** message, the slave will start transmitting
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**DATA** messages until the master sends a **STOP_CMD**. The master will send
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the **STOP_CMD** after receiving N **DATA** messages from the slave (N = 50 by
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default).
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5. When the slave receives the **STOP_CMD**, it will confirm that it has stopped
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by sending a **STOP_RESP** message to the master.
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## External Transceiver and Pin Assignment
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The CAN controller in the ESP32 **does not contain an internal transceiver**.
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Therefore users are responsible for providing an external transceiver compatible
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with the physical layer specifications of their target ISO standard (such as
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SN65HVD23X transceivers for ISO 11898-2 compatibility)
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The CAN controller in the ESP32 represents dominant bits to the transceiver as
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logic low, and recessive bits as logic high. The Network Example utilizes the
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following default pin assignments
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* TX Pin is routed to GPIO21
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* RX Pin is routed to GPIO22
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The following diagram illustrates an example network
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~~~~
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---------- ---------- --------------
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| Master | | Slave | | Listen Only |
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| 21 22 | | 21 22 | | 21 22 |
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---------- ---------- --------------
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---------- ---------- ----------
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| D R | | D R | | D R |
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| VP230 | | VP230 | | VP230 |
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| H L | | H L | | H L |
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---------- ---------- ----------
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|--x------|-----x------|-----x------|--| H
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|---------x------------x------------x--| L
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~~~~
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## Note
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If there appears to be no activity on the CAN bus when running the example, users
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can try running the `can_self_test` example to verify if their transceivers are
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wired properly.
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