The MCP2515-I/ST contains three main functional blocks: the CAN protocol engine, the message filtering and buffer management logic, and the SPI interface module. The CAN protocol engine handles bit timing, bit stuffing, CRC generation/checking, error management, and frame transmission/reception according to CAN 2.0B specifications. When the host MCU wants to transmit a message, it writes the identifier, data length, and data bytes into one of the three transmit buffers via the SPI interface, then sets the corresponding transmit request bit. The CAN engine selects the highest-priority buffer and transmits the frame on the bus. For reception, incoming messages are checked against the acceptance filters and masks; matching messages are stored in one of the two receive buffers. The first two data bytes can also be filtered, enabling protocol-specific message discrimination. When a valid message is received, the interrupt pin (INT) asserts to notify the host MCU. The one-shot mode ensures a message is only transmitted once per request, useful for time-triggered CAN protocols. The CLKOUT pin provides a programmable clock output derived from the oscillator for system use.