38.7.7 Nominal Bit Timing and Prescaler

This register is write-restricted and writable only if both CCCR.CCE bit (CCCR <1>) and CCCR.INIT bit (CCCR <0>) are set.

The CAN bit time may be programmed in the range of 4 to 385 time quanta. The CAN time quantum may be programmed in the range of 1 to 512 GCLK_CANx periods. tq = (NBRP + 1) mtq.

Therefore the length of the bit time is [NTSEG1 + NTSEG2 + 3] tq, where NTSEG1 and NTSEG2 are programmed values in the NBTP register.

Note: With a CAN clock (GCLK_CANx) of 8MHz, the reset value 0x06000A03 configures the CAN for a bit rate of 500 kBits/s.

Table 38-24. Register Bit Attribute Legend
Symbol	Description	Symbol	Description	Symbol	Description
R	Readable bit	HC	Cleared by Hardware	(Grey cell)	Unimplemented
W	Writable bit	HS	Set by Hardware	X	Bit is unknown at Reset
K	Write to clear	S	Software settable bit	—	—

Name:	NBTP
Offset:	0x1C
Reset:	0x00000A33
Property:	Write-restricted


Bit	31	30	29	28	27	26	25	24
	NSJW[6:0]							NBRP[8]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	1	1	0


Bit	23	22	21	20	19	18	17	16
	NBRP[7:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	0	0	0	0


Bit	15	14	13	12	11	10	9	8
	NTSEG1[7:0]
Access	R/W	R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset	0	0	0	0	1	0	1	0


Bit	7	6	5	4	3	2	1	0
		NTSEG2[6:0]
Access		R/W	R/W	R/W	R/W	R/W	R/W	R/W
Reset		0	0	0	0	0	1	1

Bits 31:25 – NSJW[6:0] Nominal (Re)Syncronization Jump Width

Value	Description
0x00 - 0x7F	Valid values are 0 to 127. The actual interpretation by the hardware of this value is such that one more than the programmed value is used.

Bits 24:16 – NBRP[8:0] Nominal Baud Rate Prescaler

Value	Description
0x000 - 0x1FF	The value by which the GCLK_CANx is divided for generating the bit time quanta. The bit time is built up from a multiple of this quanta. Valid values for the Baud Rate Prescaler are 0 to 511. The actual interpretation by the hardware of this value is such that one more than the value programmed here is used.

Bits 15:8 – NTSEG1[7:0] Nominal Time segment before sample point

Value	Description
0x00 - 0x7F	Valid values are 1 to 255. The actual interpretation by the hardware of this value is such that one more than the programmed value is used. NTSEG1 is the sum of PROPAGATION TIME SEGMENT (PROP_SEG) and PHASE BUFFER SEGMENT1 (PHASE_SEG1).

Bits 6:0 – NTSEG2[6:0] Time segment after sample point

Value	Description
0x00 - 0x7F	Valid values are 0 to 127. The actual interpretation by the hardware of this value is such that one more than the programmed value is used. NTSEG2 is PHASE BUFFER SEGMENT2 (PHASE_SEG2).