T89C51CC01 Atmel, T89C51CC01 Datasheet - Page 91

• Manufacturer Part Number: T89C51CC01
• Description: Enhanced 8-Bit Microcontroller
• Manufacturer: Atmel

Figure 48. General Structure of a Bit Period
4129K–CAN–01/05
(1) Phase error ≤ 0
(2) Phase error ≥ 0
(3) Phase error > 0
(4) Phase error < 0
system clock
oscillator
data
Tsyns (*)
example of bit timing determination for CAN baudrate of 500kbit/s:
Fosc = 12 MHz in X1 mode => FCAN = 6 MHz
Verify that the CAN baud rate you want is an integer division of FCAN clock.
FCAN/CAN baudrate = 6 MHz/500 kHz = 12
The time quanta TQ must be comprised between 8 and 25: TQ = 12 and BRP = 0
Define the various timing parameters: Tbit = Tsyns + Tprs + Tphs1 + Tphs2 =
12TQ
Tsyns = 1TQ and Tsjw =1TQ => SJW = 0
If we chose a sample point at 66.6% => Tphs2 = 4TQ => PHS2 = 3
Tbit = 12 = 4 + 1 + Tphs1 + Tprs, let us choose Tprs = 3 Tphs1 = 4
PHS1 = 3 and PRS = 2
BRP = 0 so CANBT1 = 00h
SJW = 0 and PRS = 2 so CANBT2 = 04h
PHS2 = 3 and PHS1 = 3 so CANBT3 = 36h
(*) Synchronization Segment: SYNS
1/ Fcan
Tsyns = 1xTscl (fixed)
Tscl
Tbit calculation:
Tprs
one nominal bit
Bit Rate Prescaler
Tbit
Tbit
Tphs1 + Tsjw (3)
=
Tphs1 (1)
Tsyns
Sample Point
+
Tprs
Tphs2 - Tsjw (4)
+
Tphs1
Tphs2 (2)
Transmission Point
T89C51CC01
+
Tphs2
91