70353C datasheet(43/76 Pages) MICROCHIP

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DS70353C-page 21-43

Section 21. Enhanced Controller Area Network (ECAN™)

21.7

RECEIVING ECAN MESSAGES

The ECAN module can receive both standard and extended frames on the CAN bus node. This

module has the additional capability of automatically transferring the received messages to the

user-defined buffers in device RAM, thereby eliminating the need for the user application to

explicitly copy messages from hardware registers to the user-defined buffers. The storage format

of each message within the DMA buffer is identical to that of transmit buffers, with each

message (including the associated status register) occupying eight words in device RAM.

The two main stages that constitute the ECAN reception process are described below, with a

simplified reception process example illustrated in Figure 21-10 and Figure 21-13.

21.7.1

Message Reception and Acceptance Filtering

As illustrated in Figure 21-10, every incoming message on the bus is received into a Message

Assembly Buffer, and its identifier field is compared with a set of 16 user-defined acceptance

filters. Each received standard data frame contains an 11-bit SID, and each extended data frame

contains an 11-bit SID and an 18-bit EID. If all bits in the incoming identifier completely match the

corresponding bits in any of the acceptance filters, the ECAN module generates a DMA transfer

request to the DMA Controller so that the message can be received into the appropriate buffer

in device RAM.

Figure 21-10: Message Reception and Acceptance Filtering 7

SID

EID

Word 0

Word 1

Word 2

Word 3

Word 4

Word 5

Word 6

Word 7

Filter 0

Filter 1

Filter 2

Filter 3

Filter 4

Filter 5

Filter 6

Filter 7

Filter 8

Filter 9

Filter 10

Filter 11

Filter 12

Filter 13

Filter 14

Filter 15

Identifier

Comparison

ECAN™ Data Frames

Filter Match (DMA Transfer Request)

Message

Assembly

Buffer

Acceptance

Filters (0-15)

User-Defined

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