Mask Function - NEC V850ES/F 3-L Series User Manual

Chapter 18

18.9.4 Mask function

Note
606
For any message buffer, which is used for reception, the assignment to one of
four global reception masks (or no mask) can be selected.
By using the mask function, the message ID comparison can be reduced by
masked bits, herewith allowing the reception of several different IDs into one
buffer.
While the mask function is in effect, an identifier bit that is defined to be 1 by a
mask in the received message is not compared with the corresponding
identifier bit in the message buffer.
However, this comparison is performed for any bit whose value is defined as 0
by the mask.
For example, let us assume that all messages that have a standard-format ID,
in which bits ID27 to ID25 are 0 and bits ID24 and ID22 are 1, are to be stored
in message buffer 14. The procedure for this example is shown below.
1. Identifier to be stored in message buffer
ID28 ID27 ID26
x 0 0
2. Identifier to be configured in message buffer 14 (example)
(Using CnMIDL14 and CnMIDH14 registers)
ID28 ID27 ID26
x 0 0
ID17 ID16 ID15
x x x
ID6 ID5 ID4
x x x
1. ID with the ID27 to ID25 bits cleared to 0 and the ID24 and ID22 bits set to
1 is registered (initialized) to message buffer 14.
2. Message buffer 14 is set as a standard format identifier that is linked to
mask 1 (MT[2:0] of CnMCONF14 register are set to 010
Mask setting for CAN module 0(mask 1) (example)
(Using CAN0 address mask 1 registers L and H (C0MASKL1 and C0MASKH1))
CMID28 CMID27 CMID26 CMID25
1 0 0
CMID17 CMID16 CMID15 CMID14
1 1 1
CMID6 CMID5 CMID4
1 1 1
1: Not compared (masked)
0: Compared
User's Manual U18743EE1V2UM00
ID25 ID24 ID23 ID22
0 1 x
ID25 ID24 ID23 ID22
0 1 x
ID14 ID13 ID12 ID11
x x x
ID3 ID2 ID1 ID0
x x x
CMID24 CMID23 CMID22
0 0 1
CMID13 CMID12 CMID11
1 1 1
CMID3 CMID2 CMID1 CMID0
1 1 1
CAN Controller (CAN)
ID21 ID20 ID19
1 x x x
ID21 ID20 ID19
1 x x x
ID10 ID9 ID8
x x x x
x
).
B
CMID21 CMID20 CMID19
0 1 1 1
CMID10 CMID9 CMID8
1 1 1 1
1
ID18
x
ID18
x
ID7
x
CMID18
1
CMID7
1