MXC1050

CAN 2.0A uses 11-bit identifiers (standard format) supporting 2048 unique message IDs. CAN 2.0B uses 29-bit identifiers (extended format) supporting over 536 million unique IDs. MXC1050 supports both formats (CAN 2.0B passive for 2.0A compatibility, and full 2.0B). Most modern systems use CAN 2.0B for the larger address space. CAN 2.0A is sufficient for simple networks with few nodes. The identifier determines message priority - lower numerical ID has higher priority. Both formats use the same physical layer and data rates. MXC1050 automatically handles both formats without configuration.

Use CAN 2.0B for new designs with large networks. Use CAN 2.0A for simple systems with few nodes.

CAN uses non-destructive bitwise arbitration to resolve bus access conflicts. When multiple nodes transmit simultaneously, the node with the highest priority message (lowest identifier) wins arbitration. Process: All nodes start transmitting their identifier bits simultaneously. Each transmitting node monitors the bus. If a node transmits a recessive bit (1) but sees a dominant bit (0), it loses arbitration and stops transmitting. The winning node continues transmitting its complete message. This ensures the highest priority message is always transmitted without delay or data corruption. After the winning message completes, losing nodes automatically retry. This built-in priority system makes CAN ideal for real-time systems.

Assign lower ID values to higher priority messages. Arbitration is automatic and transparent to application.

CAN bus requires termination at both ends of the bus to prevent signal reflections. Standard termination: 120Ω resistor at each end of the bus, matching cable characteristic impedance (typically 120Ω for CAN). Split termination (two 60Ω resistors with capacitor to ground at center) provides better EMI performance and common-mode filtering. For short buses (<10m) at low speeds (<125kbps), termination may be reduced or omitted, but this is not recommended for reliable operation. Each node should not have termination - only at physical ends of bus. Improper termination causes signal reflections, data errors, and reduced noise immunity. Always use proper termination for reliable CAN operation.

Use 120Ω termination at both ends. Consider split termination for EMI-critical applications.

CAN is designed to handle ground potential differences up to ±12V (MXC1050 specification). The differential signaling rejects common-mode noise and ground shifts. For larger ground differences or safety isolation: 1) Use isolated CAN transceivers (MXC1050I with 5kV isolation). 2) Use external CAN isolator modules. 3) Use fiber optic CAN converters for very large isolation requirements. Isolation is recommended when: Connecting equipment in different buildings, safety requirements mandate isolation, ground loops are causing problems, high-voltage present on one side of network. Isolated CAN maintains all protocol features while providing galvanic isolation.

Standard CAN handles ±12V ground shift. Use isolated CAN for larger differences or safety requirements.

CAN includes sophisticated fault confinement to prevent faulty nodes from disrupting the network. Each CAN controller maintains transmit and receive error counters. States: 1) Error Active (normal operation) - counters < 128, node transmits active error flags. 2) Error Passive - counters ≥ 128, node transmits passive error flags (less disruptive). 3) Bus Off - transmit counter ≥ 256, node disconnected from bus. Error counter increments on detected errors, decrements on successful transmissions. This automatic fault confinement prevents a single faulty node from continuously disrupting communication. Faulty nodes automatically recover when error condition clears. MXC1050 provides error flag outputs for monitoring bus health.

Fault confinement is automatic. Monitor error flags for system diagnostics. Design system to handle bus-off recovery.