CAN Bus Transceiver Symbol
Definition: The CAN Bus Transceiver symbol represents an integrated circuit — such as the Microchip MCP2551 or TI SN65HVD230 — that interfaces a microcontroller's single-ended CAN TX/RX logic to the differential CAN bus (CANH/CANL wire pair) defined by ISO 11898-2, converting logic-level signals to the differential voltage levels required for noise-immune communication on the CAN network.
Also known as: CAN transceiver, CAN bus transceiver, MCP2551, TI SN65HVD230, ISO 11898 transceiver, CAN physical layer IC.
What the CAN Bus Transceiver symbol means
The CAN Bus Transceiver symbol represents the physical-layer interface chip between a microcontroller or CAN controller and the two-wire differential CAN bus. On the left side, the TXD pin accepts the transmit data signal from the microcontroller and the RXD pin sends received bus data back to the microcontroller. On the right side, CANH and CANL connect to the differential bus cable with the characteristic 120 Ω termination resistors at each end of the bus.
The transceiver performs signal conversion in both directions: during transmission it drives the bus to a dominant state (CANH ≈ 3.5 V, CANL ≈ 1.5 V, differential ≈ 2 V) when TXD is low, and releases the bus to the recessive state (CANH = CANL ≈ 2.5 V, differential ≈ 0 V) when TXD is high. During reception it monitors the differential bus voltage and sets RXD low (dominant) or high (recessive) accordingly, providing electrical isolation and common-mode noise rejection for the microcontroller.
How to identify the CAN Bus Transceiver symbol
The CAN Bus Transceiver is drawn as a rectangular IC block with four labelled pins: TXD and RXD on the left side (connecting to the microcontroller / CAN controller), and CANH and CANL on the right side (connecting to the differential bus cable). The designator is typically U or IC in schematics. The block may include the chip part number (e.g. MCP2551) as an annotation.
Function in a circuit
The CAN transceiver IC acts as the physical-layer driver and receiver for the CAN bus (Controller Area Network), providing the differential signalling required by ISO 11898-2 for high noise immunity at data rates up to 1 Mbit/s over cable lengths up to 40 metres (at 1 Mbit/s) or 500 metres (at 125 kbit/s). It also provides bus short-circuit protection, thermal shutdown, and protection against bus wire faults, isolating the microcontroller from bus voltage transients.
Standards: IEC vs ANSI
| IEC 60617 | ISO 11898-2 defines the CAN high-speed physical layer including the differential signalling levels, driver/receiver characteristics, and 120 Ω termination. ISO 11898-1 defines the CAN data link and physical signalling layers. The transceiver IC is the hardware implementation of the ISO 11898-2 physical medium attachment (PMA) sublayer. |
|---|---|
| ANSI/IEEE 315 | SAE J1939-11 (for heavy vehicles) and ISO 11898-2 are the governing standards. SAE J1939 is widely used in North American automotive and agricultural equipment. The symbol follows IEEE 315 / ANSI Y32.2 IC symbol conventions for a rectangular block with labelled pins. |
| Key difference | The schematic symbol is functionally identical in IEC and ANSI/IEEE drawing styles — a rectangular block with named pins. The IEC style may use specific pin naming conventions from ISO 11898 documentation; ANSI/IEEE schematics follow the pin names in the IC datasheet. |
Terminals / pins
| Pin | Name |
|---|---|
| txd | TXD |
| rxd | RXD |
| canh | CANH |
| canl | CANL |
Typical values
Supply voltage: 4.5 V to 5.5 V (standard CMOS, e.g. MCP2551) or 3.0 V to 3.6 V (3.3 V variants, e.g. SN65HVD230). Bus voltage common-mode range: −7 V to +12 V (ISO 11898-2). Differential output voltage (dominant): ≥ 1.5 V. Maximum data rate: 1 Mbit/s. Bus cable impedance: 120 Ω characteristic; termination resistors 120 Ω at each end. Operating temperature: −40 °C to +125 °C (automotive grade).
Where the CAN Bus Transceiver symbol is used
- Automotive ECU networks — connecting engine control units, ABS modules, and body control modules on the vehicle CAN bus
- Agricultural and heavy machinery — SAE J1939 CAN network for ISOBUS tractor/implement communication
- Industrial automation — CANopen and DeviceNet fieldbus nodes connecting sensors, drives, and PLCs
- Medical equipment — CAN communication between modular subsystems in imaging and diagnostic devices
- Building automation — BACnet/IP over CAN physical layer for HVAC controllers
- Robotics — CAN-based motor driver communication in servo systems (e.g. DYNAMIXEL, ODRIVE)
- Prototype and embedded development — Arduino shields and Raspberry Pi HATs with MCP2515 CAN controller plus MCP2551 transceiver
Example
In a car ECU schematic, the CAN transceiver symbol sits between the microcontroller (TXD and RXD driving the left pins) and the vehicle wiring harness (CANH and CANL on the right pins), with a 120 Ω termination resistor across CANH–CANL at the end-of-bus node; the MCP2551 transceiver converts the 5 V logic signals to the ISO 11898-2 differential bus levels at up to 1 Mbit/s.
Key facts
- A CAN bus transceiver converts single-ended microcontroller TXD/RXD logic signals to and from the differential CANH/CANL bus signals defined by ISO 11898-2.
- The symbol has four pins: TXD (transmit data from controller), RXD (receive data to controller), CANH (CAN high bus wire), and CANL (CAN low bus wire).
- In the dominant bus state, CANH ≈ 3.5 V and CANL ≈ 1.5 V (differential ≈ 2 V); in the recessive state both lines float to ≈ 2.5 V (differential ≈ 0 V).
- ISO 11898-2 requires 120 Ω termination resistors at each end of the CAN bus segment; without termination, signal reflections cause communication errors at high data rates.
- Maximum data rate is 1 Mbit/s (at ≤ 40 m bus length); longer buses require lower bit rates — 500 kbit/s at 100 m, 125 kbit/s at 500 m.
- Common transceiver ICs: Microchip MCP2551 (5 V), TI SN65HVD230 (3.3 V), NXP TJA1050 (5 V automotive).
- The transceiver provides protection against bus short-circuits, thermal overload, and common-mode bus voltages up to ±12 V, isolating the microcontroller from bus faults.
Frequently asked questions
What does the CAN bus transceiver symbol mean in a schematic?
The CAN bus transceiver symbol represents an IC that acts as the physical-layer interface between a microcontroller and the differential CAN bus. The left pins (TXD, RXD) connect to the microcontroller's CAN controller; the right pins (CANH, CANL) connect to the two-wire differential bus cable. The IC converts logic-level signals to ISO 11898-2 differential bus voltages and vice versa.
What does the CAN transceiver symbol look like?
The CAN transceiver symbol is a rectangle (IC block) with four labelled pins: TXD and RXD on the left side facing the microcontroller, and CANH and CANL on the right side facing the bus cable. The part number (e.g. MCP2551 or SN65HVD230) is usually annotated inside or above the block.
What standard defines CAN bus transceiver electrical requirements?
ISO 11898-2 defines the CAN high-speed physical layer including the differential voltage levels (dominant: CANH–CANL ≥ 1.5 V; recessive: ≈ 0 V), driver output current, receiver threshold, and common-mode range. ISO 11898-1 covers the data link layer. SAE J1939-11 applies the standard to heavy vehicle CAN networks.
What is the difference between TXD/RXD and CANH/CANL pins?
TXD (transmit data) and RXD (receive data) are single-ended 3.3 V or 5 V logic signals that interface directly with the microcontroller's CAN controller peripheral. CANH and CANL are the differential bus lines that carry the actual CAN bus signal across the cable to all nodes on the network; they operate at ≈ 2.5 V common-mode with ±1 V differential swing.
Why are termination resistors required on a CAN bus?
CAN bus uses transmission line signalling at up to 1 Mbit/s; without 120 Ω termination resistors at each end of the bus, signal reflections from the unterminated ends cause voltage spikes that corrupt bit timing and trigger transmission errors. The 120 Ω value matches the characteristic impedance of a standard shielded twisted-pair CAN cable per ISO 11898-2.
How far can a CAN bus run?
ISO 11898-2 specifies a maximum bus length that decreases with increasing bit rate: approximately 40 m at 1 Mbit/s, 100 m at 500 kbit/s, 250 m at 250 kbit/s, and 500 m at 125 kbit/s. Longer runs require reduced bit rates because propagation delay must remain below 5% of the bit time for proper arbitration.
Can a CAN transceiver be used without an external CAN controller?
A CAN transceiver handles only the physical layer (signal conversion between logic and differential bus). It requires a separate CAN controller (either a dedicated IC such as MCP2515 or a built-in peripheral in microcontrollers like STM32 or ESP32) to handle the CAN protocol — framing, arbitration, error detection, and acknowledgement. The transceiver alone cannot encode or decode CAN frames.
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