CAN Transceiver

Component type: CanTransceiver

The CAN Transceiver connects one microcontroller’s CAN controller (called TWAI on Espressif chips) to a shared CAN bus. It behaves like an ideal TJA1050 or SN65HVD230: use one per node, and join all of them on one bus line.

Pins

Pin	Direction	Connect to
TXD	Input	The MCU’s CAN TX pin
RXD	Output	The MCU’s CAN RX pin
BUS	Bus line	The BUS pin of every other transceiver

A real transceiver has two bus wires, CANH and CANL. The simulator folds them into one logical line, the BUS pin, so a two-wire bus is a single wire here.

The part has no power pins and no configuration. There are no termination resistors to add.

Behaviour

• TXD low drives the bus dominant. TXD high or unwired leaves it recessive.
• The bus is wired-AND: if any node drives dominant, the bus is dominant. This is what lets CAN arbitration and ACK work.
• RXD follows the bus, including the node’s own transmissions, as on real hardware.

Wiring example

Two nodes: a Seeed XIAO ESP32-C3 and an ESP32-P4 board, each with its own transceiver.

From	To
XIAO ESP32-C3 D2 (GPIO4, TWAI TX)	Transceiver A TXD
Transceiver A RXD	XIAO ESP32-C3 D3 (GPIO5, TWAI RX)
ESP32-P4 GPIO22 (TWAI TX)	Transceiver B TXD
Transceiver B RXD	ESP32-P4 GPIO23 (TWAI RX)
Transceiver A BUS	Transceiver B BUS

XIAO ESP32-C3                                      ESP32-P4 board
  D2 (GPIO4) ──► TXD ┐                       ┌ TXD ◄── GPIO22
  D3 (GPIO5) ◄── RXD ┘ A  BUS ─────── BUS  B └ RXD ──► GPIO23

Both chips route TWAI through the GPIO matrix, so any free GPIO works. GPIO4 and GPIO5 are the defaults in ESP-IDF v5.5’s twai_network example. Add more nodes by giving each one a transceiver and wiring its BUS pin to the same net.

With ESP-IDF’s driver/twai.h, the C3 side looks like this (use GPIO_NUM_22 and GPIO_NUM_23 on the P4):

twai_general_config_t g = TWAI_GENERAL_CONFIG_DEFAULT(GPIO_NUM_4, GPIO_NUM_5, TWAI_MODE_NORMAL);
twai_timing_config_t t = TWAI_TIMING_CONFIG_500KBITS();
twai_filter_config_t f = TWAI_FILTER_CONFIG_ACCEPT_ALL();
ESP_ERROR_CHECK(twai_driver_install(&g, &t, &f));
ESP_ERROR_CHECK(twai_start());

Things to know

• A frame needs a second node to be acknowledged. A node alone on the bus, or with only listen-only nodes, gets ACK errors and keeps retransmitting while its transmit error counter rises. This is standard CAN behaviour. Put at least two nodes in normal mode on the bus.
• Every node must use the same bit rate. A node at a different rate sees error frames and disturbs the others.
• Never wire two MCUs’ TX pins straight together. Each node gets its own transceiver.

Limitations

• CANH and CANL are one logical line, so differential faults (a shorted or open CANH or CANL wire) cannot be modelled.
• No propagation delay, slope control, standby pin or supply behaviour is modelled.