Intel 87C196CB Manual De Usuario

7-21

Each message object configuration register (Figure 7-12) specifies a message identifier type
(standard or extended), transfer direction (transmit or receive), and data length (in bytes). 

Set the XTD bit for a message object with an extended identifier; clear it for a message with a
standard identifier. If you accidentally clear the XTD bit for a message that has an extended iden-
tifier, the CAN controller will clear the extended bits in the identification register. If you set the
XTD bit for a message object, that message object cannot receive message objects with standard
identifiers. 

For a transmit message, set the DIR bit and write the number of programmed data bytes (0–8) to
the DLC field. For a receive message, clear the DIR bit. The CAN controller stores the data length
from the received message in the DLC field. 

Address:
Reset State:

1E

x

6H (

x

 = 1–F)

Unchanged

Program the CAN message object 

x 

configuration (CAN_MSG

x

CFG) register to specify a message 

object’s data length, transfer direction, and identifier type.

DLC3

DLC2

DLC1

DLC0

DIR

XTD

—

—

7:4

DLC3:0

Data Length Code

Specify the number of data bytes this message object contains. Valid 
values are 0–8. The CAN controller updates a receive message object’s 
data length code after each reception to reflect the number of data bytes in 
the current message.

3

DIR

Direction

Specify whether this message object is to be transmitted or is to receive a 
message object from a remote node.

0 = receive
1 = transmit 

2

XTD

Extended Identifier Used

Specify whether this message object’s identification registers contain an 
extended (29-bit) or a standard (11-bit) identifier.

0 = standard identifier
1 = extended identifier

1:0

—

Reserved; for compatibility with future devices, write zeros to these bits.