MEGA128CAN Datasheet, PDF (236/413 Pages) ATMEL Corporation – Microcontroller WITH 128K BYTES OF ISP FLASH AND CAN CONTROLLER

Figure 117. Sample and Transmission Point
Bit Timing
PRS (3-bit length)
CLK_IO
Prescaler BRP
Fcan (Tscl)
Time Quantum
PHS1 (3-bit length)
PHS2 (3-bit length)
SJW (2-bit length)
Figure 118. General Structure of a Bit Period
CLK_IO
F_CAN
/1
CLK _IO
Tscl (TQ)
Bit Rate Prescaler
Sample
Point
Transmission
Point
Data
one nominal bit
(1) Phase error ≤ 0
(2) Phase error ≥ 0
(3) Phase error > 0
(4) Phase error < 0
Tsyns(*)
Tprs
Tphs1 (1)
Tphs1+Tsjw (3)
Tbit
Tphs2 (2)
Tphs2+Tsjw (4)
(*) Synchronization Segment: SYNS
Tsyns=1xTscl (fixed)
Sample
Point
Transmission
Point
Baud Rate
The baud rate selection is made by T_bit calculation:
Tbit⁽¹⁾ = Tsyns + Tprs + Tphs1 + Tphs2
1. Tsyns = 1 x Tscl = (BRP[5..0]+ 1)/clk_IO (= 1TQ)
2.Tprs = (1 to 8) x Tscl = (PRS[2..0]+ 1) x Tscl
3.Tphs1 = (1 to 8) x Tscl = (PHS1[2..0]+ 1) x Tscl
4.Tphs2 = (1 to 8) x Tscl = (PHS2[2..0]⁽²⁾+ 1) x Tscl
5.Tsjw = (1 to 4) x Tscl = (SJW[1..0]+ 1) x Tscl
Notes: 1. The total number of Tscl (Time Quanta) in a bit time must be between 8 to 25.
2. PHS2[2..0] 2 is programmable to be maximum of PHS1[2..0] and 1.
Fault Confinement
(c.f. Section “Error Management”).
236 AT90CAN128
4250E–CAN–12/04