LM3S2637 Datasheet, PDF (558/678 Pages) Texas Instruments – Stellaris® LM3S2637 Microcontroller

Controller Area Network (CAN) Module
tPhase1 = 2 * t_q
tPhase2 = 2 * t_q
\\tPhase2 = tPhase1
tTSeg1 = tProp + tPhase1
tTSeg1 = (3 * t_q) + (2 * t_q)
tTSeg1 = 5 * t_q
tTSeg2 = tPhase2
tTSeg2 = (Information Processing Time + 2) × t_q
tTSeg2 = 2 * t_q
\\Assumes IPT=0
tSJW = 2 * t_q
\\Least of 4, Phase1 and Phase2 = 1
In the above example, the bit field values for the CANBIT register are:
TSEG2
TSEG1
SJW
BRP
= TSeg2 -1
= 2-1
=1
= TSeg1 -1
= 5-1
=4
= SJW -1
= 2-1
=1
= Baud rate prescaler - 1
= 1-1
=0
The final value programmed into the CANBIT register = 0x1440.
15.3.16.2 Example for Bit Timing at Low Baud Rate
In this example, the frequency of the CAN clock is 8 MHz, and the bit rate is 100 Kbps.
bit time = 10 µs = n * t_q = 10 * t_q
t_q = 1 µs
t_q = (Baud rate Prescaler)/CAN Clock
Baud rate Prescaler = t_q * CAN Clock
Baud rate Prescaler = 1E-6 * 8E6 = 8
tSync = 1 * t_q = 1 µs
\\fixed at 1 time quanta
delay of bus driver 200 ns
delay of receiver circuit 80 ns
delay of bus line (40m) 220 ns
tProp 1 µs = 1 * t_q
\\1 µs is next integer multiple of t_q
bit time = tSync + tTSeg1 + tTSeg2 = 10 * t_q
bit time = tSync + tProp + tPhase 1 + tPhase2
tPhase 1 + tPhase2 = bit time - tSync - tProp
tPhase 1 + tPhase2 = (10 * t_q) - (1 * t_q) - (1 * t_q)
tPhase 1 + tPhase2 = 8 * t_q
tPhase1 = 4 * t_q
558
June 18, 2012
Texas Instruments-Production Data