ST STM8S Reference Manual

RM0016 Controller area network (beCAN)
Doc ID 14587 Rev 8 371/449
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 146. 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.
EMPTY
Valid Message
FMP = 00b
FOVR = 0
PENDING_1
FMP = 01b
FOVR = 0
Received
PENDING_2
FMP = 10b
FOVR = 0
PENDING_3
FMP = 11b
FOVR = 0
Valid Message
Received
Release
OVERRUN
FMP = 11b
FOVR = 1
Mailbox
Release
Mailbox
Valid Message
Received
Valid Message
Received
Release
Mailbox
Release
Mailbox
Valid Message
Received
RFOM = 1
RFOM = 1
RFOM = 1

ST STM8S Specifications

General

Brand	ST
Model	STM8S
Category	Microcontrollers
Language	English