Datasheet

Figure 20-8. General Structure of a bit period
 
Bit rate
prescaler
CLK
IO
F
CAN
Data
Tscl (TQ)
1
/
CLK
IO
One nominal bit
Tsyns(5)
Tphs2+Tsjw (
4 )Tphs1+Tsjw ( 3 )
Tbit
Tphs2 (
2 )Tphs1 ( 1 )Tprs
Sample
point
Transmission
point
5. Synchronization segment: SYNS
Tsyns = 1
x Tscl ( fixed )
Notes: 1. Phase error < 0
2. Phase error > 0
3. Phase error > 0
4. Phase error < 0
or or
20.5.3. Baud rate
With no baud rate prescaler (BRP[5..0]=0) the sampling point comes one time quantum too early. This
leads to a fail according the ISO16845 Test plan. It is necessary to lengthen the Phase Segment 1 by one
time quantum and to shorten the Phase Segment 2 by one time quantum to compensate. The baud rate
selection is made by T
bit
calculation:
Tbit
(1)
= Tsyns + Tprs + Tphs1 + Tphs2
1. Tsyns = 1 × Tscl = (BRP[5..0] + 1)/clk
IO
(= 1TQ)
2. Tprs = (1 to 8) × Tscl = (PRS[2..0] + 1) × Tscl
3. Tphs1 = (1 to 8) × Tscl = (PHS1[2..0] + 1) × Tscl
4. Tphs2 = (1 to 8) × Tscl = (PHS2[2..0]
(2)
+ 1) × Tscl
5. Tsjw = (1 to 4) × Tscl = (SJW[1..0] + 1) × Tscl
Notes: 1. The total number of Tscl (Time Quanta) in a bit time must be from 8 to 25.
2. PHS2[2..0] 2 is programmable to be ≤ PHS1[2..0] and ≥1.
20.5.4. Fault confinement
See Error management.
20.5.5. Overload frame
An overload frame is sent by setting an overload request (OVRQ). After the next reception, the CAN
channel sends an overload frame in accordance with the CAN specification. A status or flag is set (OVRF)
as long as the overload frame is sent.
Atmel ATmega16M1/32M1/64M1 [DATASHEET]
Atmel-8209F-ATmega16M1/32M1/64M1_Datasheet_Complete-10/2016
232