Intel 87C196CB, 8XC196NT user manual Programming the Bit Timing 0 CANBTIME0 Register, CANBTIME0 †

CAN SERIAL COMMUNICATIONS CONTROLLER

7.4.2Programming the Bit Timing 0 (CAN_BTIME0) Register

Bit timing register 0 (Figure 7-7) defines the length of one time quantum and the maximum

amount by which the sample point can be moved (tTSEG1 or tTSEG2 can be shortened and the other lengthened) to compensate for resynchronization.

CAN_BTIME0 †	Address:	1E3FH
(87C196CB)	Reset State:	Unchanged

Program the CAN bit timing 0 (CAN_BTIME0) register to define the length of one time quantum and the maximum number of time quanta by which a bit time can be modified for resynchronization.

87C196CB

7

SJW1 SJW0 BRP5 BRP4

0

BRP3 BRP2 BRP1 BRP0

Bit	Bit		Function
Number	Mnemonic
7:6	SJW1:0	Synchronization Jump Width
		This field defines the maximum number of time quanta by which a resyn-
		chronization can modify tTSEG1 and tTSEG2. Valid programmed values are 0–
		3. The hardware adds 1 to the programmed value, so a “1” value causes
		the CAN peripheral to add or subtract 2 time quanta, for example. This
		adjustment has no effect on the total bit time; if tTSEG1 is increased by 2 tq,
		tTSEG2 is decreased by 2 tq, and vice versa.
5:0	BRP5:0	Baud-rate Prescaler
		This field defines the length of one time quantum (tq), using the following
		formula, where tXTAL1 is the input clock period on XTAL1. Valid programmed
		values are 0–63.
		tq = 2tXTAL1 × (BRP + 1)
		For example, at 20 MHz operation, the system clock period is 50 ns.
		Writing 3 to BRP achieves a time quanta of 400 ns; writing 1 to BRP
		achieves a time quanta of 200 ns.
		tq = (2 × 50) × (3 + 1)	= 400 ns
		tq = (2 × 50) × (1 + 1)	= 200 ns

†The CCE bit (CAN_CON.6) must be set to enable write access to this register.

Figure 7-7. CAN Bit Timing 0 (CAN_BTIME0) Register

7-15