CAN Bus

The board uses a TJA1051T/3 CAN transceiver to provide CAN 2.0 and CAN FD tolerant (ISO 11898-2:2016) connectivity. The “/3” suffix denotes the V_IO variant, which provides level-shifted TXD and RXD logic pins that directly match the ESP32-S3’s 3.3V GPIO levels without requiring an external level shifter. The ESP32-S3 includes a built-in TWAI (Two-Wire Automotive Interface) peripheral that handles the CAN protocol in hardware, including arbitration, error detection, and automatic retransmission. The TJA1051T/3 provides the physical layer, translating between the microcontroller’s logic-level signals and the differential CAN bus signaling. The interface is exposed on a 3-pin screw terminal carrying CANH, CANL, and GND.

CAN bus was designed by Bosch in the 1980s for automotive wiring harnesses, and its fundamental properties — deterministic arbitration, built-in error handling, and multi-master architecture — have made it the backbone of automotive, industrial, and robotics communication ever since.

Pin Connections

Signal	GPIO	Description
CAN TX	IO15	TWAI TX to TJA1051T
CAN RX	IO16	TWAI RX from TJA1051T

Wiring

Connect CANH to CANH and CANL to CANL between nodes. CAN bus requires 120 ohm termination at both physical ends of the bus. The board includes an onboard 120 ohm termination resistor with jumper selection at position 19 (default: OFF). Place the jumper cap to enable termination.

Note

CAN bus is a multi-master protocol. Every message is broadcast to all nodes on the bus. Unlike RS-485, CAN handles arbitration in hardware — when two nodes transmit simultaneously, the node with the higher-priority (lower numerical) message ID wins arbitration and continues uninterrupted, while the other backs off and retries automatically. This makes CAN exceptionally robust for systems where multiple controllers share a bus.

ESD Protection

The CAN bus lines are protected by SM24CANB TVS diodes, providing protection against surge events and ESD discharge on the bus wiring.

Transceiver Specifications

The TJA1051T/3 is an AEC-Q100 qualified CAN transceiver from NXP, designed for automotive and industrial applications where reliability under extreme conditions is non-negotiable.

Parameter	Value
Part number	TJA1051T/3/1J
Standard	ISO 11898-2:2016 (CAN FD tolerant)
Qualification	AEC-Q100 Grade 1 (-40 to +125 C)
Supply voltage (VCC)	4.5V to 5.5V
I/O level voltage (V_IO)	1.8V to 5.5V
Data rate	Up to 5 Mbit/s (CAN FD)
Bus pin voltage tolerance	-58V to +58V
Loop delay (TXD to RXD)	200 ns typical
Dominant timeout	2.5 ms to 7 ms
Operating modes	Normal, Silent
Standby current	< 10 uA

The V_IO pin is what distinguishes the “/3” variant from the base TJA1051T. The base part requires 5V logic levels on TXD and RXD, which would necessitate a level shifter between the transceiver and the ESP32-S3’s 3.3V GPIOs. The “/3” variant accepts a separate V_IO supply (1.8V to 5.5V) that sets the logic-level reference for TXD and RXD. On this board, V_IO is connected to 3.3V, allowing direct connection to the ESP32-S3 without any additional circuitry.

Note

The TJA1051T/3 is CAN FD tolerant — it can handle the faster data-phase bit rates (up to 5 Mbit/s) used in CAN FD frames. However, the ESP32-S3’s TWAI peripheral only supports classical CAN 2.0 (up to 1 Mbit/s), not CAN FD. The transceiver is CAN FD ready, but the microcontroller is the limiting factor. If CAN FD is required, an external CAN controller with FD support (such as the MCP2518FD) would need to be connected via SPI.

Operating Modes

The TJA1051T/3 supports two operating modes, selected by the S (silent) pin:

• Normal mode: S pin held LOW (connected to GND on this board). Both the transmitter and receiver are active, allowing the node to send and receive frames and participate fully in bus arbitration and acknowledgment. This is the default configuration.
• Silent mode: S pin held HIGH. The receiver remains active but the transmitter is disabled — the transceiver cannot drive the bus. This mode is useful for bus monitoring and sniffing applications where the node should observe traffic without participating in arbitration or acknowledging frames. A node in silent mode is invisible to other bus participants.

On this board, the S pin is tied to GND, permanently selecting Normal mode. To use Silent mode, the S pin trace would need to be cut and routed to a GPIO for software control.

Safety Features

The TJA1051T/3 incorporates several protection mechanisms that make it suitable for safety-critical applications in automotive and industrial environments:

• TXD dominant timeout: If TXD is held dominant (LOW) for longer than 2.5 to 7 ms, the transceiver automatically releases the bus to recessive state. This prevents a single faulting node — whether due to a software hang, latch-up, or oscillator failure — from blocking all communication on the bus. In a network of dozens of ECUs, one stuck transmitter would otherwise silence every other node.
• Undervoltage detection: The transceiver monitors VCC and disables its output driver if the supply drops below the undervoltage lockout threshold. This prevents malformed or indeterminate bus signals during power-up, brown-out, or supply transient events that could corrupt frames in transit.
• Thermal protection: An internal thermal shutdown circuit disables the transmitter if the die temperature exceeds safe operating limits, protecting both the transceiver and the bus from damage during sustained fault conditions.
• Bus pin protection: Both CANH and CANL pins tolerate voltages from -58V to +58V, providing robust protection against wiring faults, ground offset between nodes, and transient events in electrically harsh environments such as automotive wiring harnesses and industrial machinery.

Common CAN Bit Rates

Bit Rate	Max Bus Length	ESP-IDF Timing Macro
125 kbit/s	500 m	TWAI_TIMING_CONFIG_125KBITS()
250 kbit/s	250 m	TWAI_TIMING_CONFIG_250KBITS()
500 kbit/s	100 m	TWAI_TIMING_CONFIG_500KBITS()
1 Mbit/s	25 m	TWAI_TIMING_CONFIG_1MBITS()

The relationship between bit rate and maximum bus length is governed by the propagation delay of the electrical signal along the cable and the requirement that all nodes sample each bit at the same point in time. Higher bit rates demand shorter cables.

Code Examples

Transmit

This example initializes the TWAI peripheral at 500 kbit/s and sends a standard CAN frame with ID 0x123 every second.

#include "driver/twai.h"

#define CAN_TX_PIN  15
#define CAN_RX_PIN  16

void setup() {
  Serial.begin(115200);

  twai_general_config_t g_config = TWAI_GENERAL_CONFIG_DEFAULT(
    (gpio_num_t)CAN_TX_PIN, (gpio_num_t)CAN_RX_PIN, TWAI_MODE_NORMAL);
  twai_timing_config_t t_config = TWAI_TIMING_CONFIG_500KBITS();
  twai_filter_config_t f_config = TWAI_FILTER_CONFIG_ACCEPT_ALL();

  if (twai_driver_install(&g_config, &t_config, &f_config) == ESP_OK) {
    Serial.println("TWAI driver installed");
  }
  twai_start();
}

void loop() {
  twai_message_t msg = {
    .identifier = 0x123,
    .data_length_code = 8,
    .data = {0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07, 0x08}
  };

  if (twai_transmit(&msg, pdMS_TO_TICKS(1000)) == ESP_OK) {
    Serial.println("Message sent");
  } else {
    Serial.println("Send failed");
  }
  delay(1000);
}

Receive

This example waits for incoming CAN frames and prints their ID, DLC, and payload bytes to the serial monitor.

#include "driver/twai.h"

#define CAN_TX_PIN  15
#define CAN_RX_PIN  16

void setup() {
  Serial.begin(115200);

  twai_general_config_t g_config = TWAI_GENERAL_CONFIG_DEFAULT(
    (gpio_num_t)CAN_TX_PIN, (gpio_num_t)CAN_RX_PIN, TWAI_MODE_NORMAL);
  twai_timing_config_t t_config = TWAI_TIMING_CONFIG_500KBITS();
  twai_filter_config_t f_config = TWAI_FILTER_CONFIG_ACCEPT_ALL();

  twai_driver_install(&g_config, &t_config, &f_config);
  twai_start();
  Serial.println("TWAI receiver ready");
}

void loop() {
  twai_message_t msg;
  if (twai_receive(&msg, pdMS_TO_TICKS(1000)) == ESP_OK) {
    Serial.printf("ID: 0x%03X DLC: %d Data:", msg.identifier, msg.data_length_code);
    for (int i = 0; i < msg.data_length_code; i++) {
      Serial.printf(" %02X", msg.data[i]);
    }
    Serial.println();
  }
}

Troubleshooting

Caution

CAN requires at least two nodes on the bus. A single node transmitting without a receiver will report errors because no ACK bit is received. The TWAI peripheral will enter an error state and eventually go bus-off. For bench testing with a single board, use TWAI_MODE_NO_ACK in the general config to suppress ACK checking.

Tip

If CAN reception fails when using UCANV2.0 software on a connected PC adapter, try restarting the COM port connection. Also, if using a serial debugger simultaneously, uncheck the DTR checkbox — DTR can interfere with the auto-download circuit and cause unexpected resets.

Bus-Off Recovery

If the TWAI peripheral enters the bus-off state (too many errors), call twai_initiate_recovery() followed by twai_start() to bring it back online. Common causes include incorrect bit rate, missing termination, or wiring faults.

Message Filtering

The TWAI_FILTER_CONFIG_ACCEPT_ALL() macro accepts every frame on the bus. For production systems, configure acceptance filters to reduce interrupt load by only accepting message IDs your node cares about.