Motorola MCF5282 Free Running Timer Timer, Rx Mask Registers, 14describes the Timer fields

Programmer’s Model

25.5.6 Free Running Timer (TIMER)

Field

Reset

R/W Address

15 0

TIMER

0000_0000_0000_0000

R/W

IPSBAR + 0x1C_000A

Figure 25-11. Free Running Timer (TIMER)

Table 25-14describes the TIMER fields.

Table 25-14. TIMER Field Descriptions

Bits	Name	Description
15–0	TIMER	The free running timer counter can be read and written by the CPU. The timer starts from zero after
		reset, counts linearly to 0xFFFF, and wraps around.
		The timer is clocked by the FlexCAN bit-clock. During a message, it increments by one for each bit that
		is received or transmitted. When there is no message on the bus, it increments at the nominal bit rate.
		The timer value is captured at the beginning of the identifier field of any frame on the CAN bus. The
		captured value is written into the “time stamp” entry in a message buffer after a successful reception
		or transmission of a message.

25.5.7 Rx Mask Registers

These registers are used as acceptance masks for received frame IDs. 3 masks are defined: A global mask, used for Rx buffers 0-13, and 2 more separate masks for buffers 14 and 15.

Mask bit = 0: The corresponding incoming ID bit is “don’t care”.

Mask bit = 1: The corresponding ID bit is checked against the incoming ID bit, to see if a match exists.

Note that these masks are used both for Standard and Extended ID formats. The value of mask registers should NOT be changed while in normal operation, as locked frames which matched a MB through a mask, may be transferred into the MB (upon release) but may no longer match.

Table 25-15. Mask examples for Normal/Extended Messages

		Base ID	I		Extended ID
			D			Match
	ID28	.................ID18		ID17	......................................ID0
			E
MB2-Id	1 1 1 1 1 1 1 1 0 0 0		0
MB3-Id	1 1 1 1 1 1 1 1 0 0 0		1	0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1
MB4-Id	0 0 0 0 0 0 1 1 1 1 1		0
MB5-Id	0 0 0 0 0 0 1 1 1 0 1		1	0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

25-26 MCF5282 User’s Manual MOTOROLA