STM8S datasheet(387/467 Pages) STMICROELECTRONICS

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RM0016

Controller area network (beCAN)

427

23.6.2

Reception handling

For the reception of CAN messages, three mailboxes organized as a FIFO are provided. In

order to save CPU load, simplify the software and guarantee data consistency, the FIFO is

managed completely by hardware. The application accesses the messages stored in the

FIFO through the FIFO output mailbox.

Valid message

A received message is considered as valid when it has been received correctly according to

the CAN protocol (no error until the last but one bit of the EOF field) and It passed through

the identifier filtering successfully, see Section 23.6.3: Identifier filtering.

Figure 147. Receive FIFO states

FIFO management

Starting from the empty state, the first valid message received is stored in the FIFO which

becomes pending_1. The hardware signals the event setting the FMP[1:0] bits in the

CAN_RFR register to the value 0b01. The message is available in the FIFO output mailbox.

The software reads out the mailbox content and releases it by setting the RFOM bit in the

CAN_RFR register. The FIFO becomes empty again. If a new valid message has been

received in the meantime, the FIFO stays in pending_1 state and the new message is

available in the output mailbox.

STM8S Datasheet(PDF) 387 Page - STMicroelectronics