7630 datasheet(120/238 Pages) RENESAS

120 / 238 page

7630 Group User’s Manual

2-54

$33/,&$7,21

2.4 Controller Area Network (CAN) module

2.4.7 Acceptance filtering

The module contains a hardware filtering circuit to screen out the useless messages out of the message stream

and thereby reduce CPU load. This filter probes the identifier field of any frame on the bus and decides which

frames are relevant to the given node and which may be abandoned.

(1) Register structure

The hardware implements a single condition identifier filter by a set of acceptance code CACi (Figures 2.4.6

to 2.4.10) and acceptance mask CAMi (Figures 2.4.11 to 2.4.15) registers. These registers cover the entire

29-bit identifier scale (extended format); however 11-bit identifiers (standard format) can be handled as well.

The registers (shown in Figure 2.4.30) can be modified in configuration mode (refer to section 2.4.5) only.

Fig. 2.4.30 Structure of acceptance mask/code registers

(2) Operation

Acceptance filtering starts after detecting the start-of-frame of a CAN message. The content of the accept-

ance mask registers define which identifier bits have to be subjected to comparison with the corresponding

bits of the acceptance code registers.

If the acceptance filter judges an incoming frame relevant, the frame is—depending on the availability of a

receive buffer—either stored in a receive buffer or a CAN overrun interrupt (COVR) is issued by setting the

corresponding interrupt request bit. For further details on the receive buffer system and the overrun interrupt

refer to sections 2.4.8 and 2.4.11.

(3) Schematic of acceptance filter

The acceptance filter mechanism (see Figure 2.4.31) comprises one gate which compares the acceptance

code register bit with the corresponding identifier bit of the frame being received, and one gate which tests

the relevance of this bit for the acceptance filter process. When all acceptance bits are true, the module rates

the frame relevant and attempts to store it to a receive buffer.

Address

CSID10

CSID9

CSID8

CSID7

CSID6

CSID5

CSID4

CSID3

CSID2

CSID1

CSID0

CEID17

CEID16

CEID15

CEID14

CEID13

CEID12

CEID11

CEID10

CEID9

CEID8

CEID7

CEID6

CEID5

CEID4

CEID3

CEID2

CEID1

CEID0

MSID10

MSID9

MSID8

MSID7

MSID6

MSID5

MSID4

MSID3

MSID2

MSID1

MSID0

MEID17 MEID16 MEID15 MEID14

MEID13 MEID12 MEID11 MEID10

MEID9

MEID8

MEID7

MEID6

MEID5

MEID4

MEID3

MEID2

MEID1

MEID0

003316

003416

003516

003616

003716

003816

003916

003A16

003B16

003C16

Acceptance code

registers:

Acceptance mask

registers:

Select the bit pattern of identifiers which should pass acceptance filtering.

0 : Mask identifier bit

1 : Compare identifier bit with acceptance code register bit

Shaded bits of CAMi must be cleared.

name

CAC0

CAC1

CAC2

CAC3

CAC4

CAM0

CAM1

CAM2

CAM3

CAM4

7630 Datasheet(PDF) 120 Page - Renesas Technology Corp

7630 Datasheet(HTML) 120 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL