CP3BT26

PRI

The Transmit

Priority Code field holds the

 

software-defined transmit priority code for the

 

message buffer.

DLC

The Data Length Code field determines the

 

number of data bytes within a received/trans-

 

mitted frame. For transmission, these bits

 

need to be set according to the number of

 

data bytes to be transmitted. For reception,

 

these bits indicate the number of valid re-

 

ceived data bytes available in the message

 

buffer. Table 53 shows the possible bit combi-

 

nations for DLC3:0 for data lengths from 0 to

 

8 bytes.

 

 

 

Table 53 Data Length Coding

 

 

 

 

 

DLC

 

Number of Data Bytes

 

 

 

 

 

0000

 

0

 

 

 

 

 

0001

 

1

 

 

 

 

 

0010

 

2

 

 

 

 

 

0011

 

3

 

 

 

 

 

0100

 

4

 

 

 

 

 

0101

 

5

 

 

 

 

 

0110

 

6

 

 

 

 

 

0111

 

7

 

 

 

 

 

1000

 

8

 

 

 

 

Note: The maximum number of data bytes received/trans- mitted is 8, even if the DLC field is set to a value greater than

8.Therefore, if the data length code is greater or equal to eight bytes, the DLC field is ignored.

19.10.2 Storage of Standard Messages

During the processing of standard frames, the Extended- Identifier (IDE) bit is clear. The ID1[3:0] and ID0[15:0] bits are “don’t care” bits. A standard frame with eight data bytes is shown in Table 54.

IDE

The Identifier Extension bit determines wheth-

 

er the message is a standard frame or an ex-

 

tended frame.

 

0

– Message is a standard frame using 11

 

 

identifier bits.

 

1

– Message is an extended frame.

RTR

The Remote Transmission Request bit indi-

 

cates whether the message is a data frame or

 

a remote frame.

 

0

– Message is a data frame.

 

1

– Message is a remote frame.

ID

The ID field is used for the 11 standard frame

 

identifier bits.

 

 

 

 

Table 54 Standard Frame with 8 Data Bytes

 

 

 

 

 

 

Address

Buffer

15

14

13

12

11

10

9

8

7

6

5

4

3

2

1

0

Register

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0XEh

ID1

 

 

 

 

ID[10:0]

 

 

 

 

 

RTR

IDE

Don’t Care

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0XCh

ID0

 

 

 

 

 

 

 

Don’t Care

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0XAh

DATA0

 

 

 

Data1[7:0]

 

 

 

 

 

 

Data2[7:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0X8h

DATA1

 

 

 

Data3[7:0]

 

 

 

 

 

 

Data4[7:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0X6h

DATA2

 

 

 

Data5[7:0]

 

 

 

 

 

 

Data6[7:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0X4h

DATA3

 

 

 

Data7[7:0]

 

 

 

 

 

 

Data8[7:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0X2h

TSTP

 

 

 

 

 

 

 

TSTP[15:0]

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0E F0X0h

CNSTAT

 

DLC

 

 

Reserved

 

 

PRI

 

 

 

 

ST

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

www.national.com

130

Page 130
Image 130
National CP3BT26 manual Data Length Coding, Dlc, Storage of Standard Messages, Rtr Ide