Controller area network (CAN) routines

UM0459

18/29

Note:

Care must be taken when defining an ID range: all combinations of idLow and idHigh will not

always produce the expected result, because of the way identifiers are filtered by hardware.

The criteria applied to keep a received frame is as follows: (received ID) AND (ID mask) =

(ID arbitration), where AND is a bitwise operator.

Consequently, for idLow, it is generally better to choose a value with some LSBs cleared,

and for idHigh, a value that “logically contains” idLow and with the same LSBs set. Example:

the range 0x100-0x3FF will work, but the range 0x100-0x2FF will not work because 0x100

is not logically contained in 0x2FF (that is: 0x100 & 0x2FF = 0).

Example:

This example illustrates how to define a 2 message FIFO and acceptance filtering:

{

/*Define a receive FIFO of depth 2 (objects 0 and 1) in CAN1 for standard

identifiers, in which IDs are filtered in the range 0x400-0x5FF*/

CAN_SetRxMsgObj(CAN1, 0, CAN_STD_ID, 0x400, 0x5FF, FALSE);

CAN_SetRxMsgObj(CAN1, 1, CAN_STD_ID, 0x400, 0x5FF, TRUE);

/*Define a single receive object for extended identifiers, in which all IDs are

filtered in*/

CAN_SetRxMsgObj(CAN1, 2, CAN_EXT_ID, 0, CAN_LAST_EXT_ID, TRUE);

}

Required preconditions

None

Called functions

CAN_GetFreeIF()

Table 15.

CAN_SetRxMsgObj function description (continued)

Function name

CAN_SetRxMsgObj