MCP25020ISLASHP datasheet(12/66 Pages) MICROCHIP

12 / 66 page

MCP2502X/5X

DS21664D-page 12

2.7

Acceptance Mask

The acceptance mask is used to define which bits in the

CAN ID are to be compared against the programmable

filters. Individual bits within the mask correspond to bits

in the CAN ID that, in turn, correspond to bits in the

acceptance filters. Any bit in the mask that is set to a ‘1’

will cause the corresponding CAN ID bit to be

compared against the associated filter bit. Any bit in the

mask that is set to a ‘0’ is not compared and effectively

sets the associated CAN ID bit to ‘don’t care’.

2.7.1

MASKS AND STANDARD/

EXTENDED IDS

To insure proper operation of the information request

and input messages, some mask bits (as configured in

the mask registers) may be ignored as explained:

Message with a standard ID - the three least

significant

bits

standard

identifier

(RXMSIDL.SID2:SID0) are ‘don’t care’ for the mask

registers and effectively become ‘0’.

Message with an extended ID - the three least

significant

bits

the

standard

identifier

(RXMSIDL.SID2:SID0) are configurable and the three

least

significant

bits

the

extended

identifier

(RXMEID0.EID2:EID0) are always ‘don’t cares’ and

effectively becomes ‘0’.

2.8

Acceptance Filters

There are two separate acceptance filters defined for

the MCP2502X/5X: RXF0 and RXF1. RXF0 is used for

Information Request messages and RXF1 is used for

input messages (see Table 4-2 and Table 4-3). Each bit

in the filters corresponds to a bit in the CAN ID. Every

bit in the CAN ID, for which the corresponding Mask bit

is set, must match the associated filter bit in order for

the message to be accepted. Messages that fail to

meet the mask/fIlter criteria are ignored.

TXIDNSIDH - TRANSMIT IDENTIFIER N STANDARD IDENTIFIER HIGH

Note:

The EXIDE bit in the Mask register

(RXMSIDL) can be used to mask the IDE

bit in the corresponding Receive buffer

R/W-x

SID10

SID9

SID8

SID7

SID6

SID5

SID4

SID3

bit 7

bit 0

bit 7-0

SID10:SID3: Standard Identifier bits

Legend:

R = Readable bit

W = Writable bit

U = Unimplemented bit, read as ‘0’

- n = Value at POR

‘1’ = Bit is set

‘0’ = Bit is cleared

x = Bit is unknown

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