Data Frame Receive Operation - Mitsubishi Electric M32R Series User Manual

Mitsubishi 32-bit risc single-chip microcomputers

Table of Contents

13.6.2 Data Frame Receive Operation

The following describes data frame receive operation. The operations described below are

automatically performed in hardware.

(1) Acceptance filtering

When the CAN module finished receiving data, it starts searching for the slot that satisfies

conditions for receiving the received message sequentially from slot 0 (up to slot 15). The

following shows receive conditions for slots that have been set for data frame reception.

[Conditions]

• The receive frame is a data frame.

• The receive ID and the slot ID are identical, assuming the ID Mask Register bits set to 0 are

"Don't care bits."

• The standard and extended frame types are the same.

Note: In BasicCAN mode, slots 14 and 15 while being set for data frame reception can also

receive remote frames.

(2) When receive conditions are met

When receive conditions in (1) above are met, the CAN module sets the CAN Message Slot

Control Register's TRSTAT (Transmit/Receive Status) and TRFIN (Transmit/Receive Finished)

bits to 1 while at the same time writing the received data to the message slot. If the TRFIN

(Transmit/Receive Finished) bit is already 1, the CAN module also sets the ML (Message Lost)

bit to 1, indicating that the message slot has been overwritten. The message slot has its ID field

and DLC field both overwritten and an indeterminate value written in its unused area (e.g.,

extended ID field for standard frame reception and an unused data field).

Furthermore, a time stamp count value at the time the message was received is written to the

CAN Message Slot Time Stamp (C0MSLnTSP) along with the received data. When the CAN

module finished writing to the message slot, it sets the CAN Slot Interrupt Status bit to 1. If the

interrupt for the slot has been enabled, an interrupt request is generated, and the slot goes to a

wait state for the next reception.

(3) When receive conditions are not met

The received frame is discarded, and the CAN module goes to the next transmit/receive

operation without writing to the message slot.

13.6 Receiving Data Frames