Intel 87C196CB User Manual

7-22

Each message identifier register (Figure 7-13) specifies the message’s identifier. For messages
with extended identifiers, write the identifier to bits ID28:0. For messages with standard identi-
fiers, write the identifier to bits ID28:18. Software can change the identifier during normal oper-
ation without requiring a subsequent device reset. Clear the MSGVAL bit in the corresponding
message control register 0 to prevent the CAN controller from accessing the message object while
the modification takes place, then set the bit to allow access.

†

Address:

Reset State:

1E

x

5H, 1E

x

4H, 

1E

x

3H, 1E

x

2H

(

x

 = 1–F)

Unchanged

Write the message object’s identifier to the CAN message object 

x

 identifier (CAN_MSG

x

ID0–3) 

register. Software can change the identifier during normal operation. Clear the MSGVAL bit in the 
corresponding CAN_MSG

x

CON0 register to prevent the CPU from accessing the message object, 

change the identifier in CAN_MSG

x

ID0–3, then set the MSGVAL bit to allow access.

CAN_MSG

x

ID3

ID4

ID3

ID2

ID1

ID0

—

—

—

CAN_MSG

x

ID2

ID12

ID11

ID10

ID9

ID8

ID7

ID6

ID5

CAN_MSG

x

ID1

ID20

ID19

ID18

ID17

ID16

ID15

ID14

ID13

CAN_MSG

x

ID0

ID28

ID27

ID26

ID25

ID24

ID23

ID22

ID21

31:27
23:16
12:8

ID4:0
ID12:5
ID17:13

Message Identifier 17:0

These bits hold the 18 least-significant bits of an extended identifier. If 
you write an extended identifier to these bits, but specify a standard 
identifier (XTD = 0) in the corresponding message object’s configuration 
register (CAN_MSG

x

CFG), the CPU clears these bits (ID17:0).

26:24

—

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

15:13
7:0

ID20:18
ID28:21

Message Identifier 28:18

These bits hold either an entire standard identifier or the 11 most-
significant bits of an extended identifier.

†

 This register is the same as the arbitration register in the standalone 82527 CAN peripheral.