176
7647H–AVR–03/12
Atmel ATmega16/32/64/M1/C1
– enables a hardware loop back, internal TxCAN on internal RxCAN
– provides a recessive level on TXCAN output pin
– does not disable RXCAN input pin
– freezes TEC and REC error counters
Figure 16-6. Listening Mode
16.4.2 Bit Timing
FSM’s (Finite State Machine) of the CAN channel need to be synchronous to the time quantum.
So, the input clock for bit timing is the clock used into CAN channel FSM’s.
Field and segment abbreviations:
• BRP: Baud Rate Prescaler.
• TQ: Time Quantum (output of Baud Rate Prescaler).
• SYNS: SYNchronization Segment is 1 TQ long.
• PRS: PRopagation time Segment is programmable to be 1, 2, ..., 8 TQ long.
• PHS1: PHase Segment 1 is programmable to be 1, 2, ..., 8 TQ long.
• PHS2: PHase Segment 2 is programmable to be ≤ PHS1 and ≥ INFORMATION
PROCESSING TIME.
• INFORMATION PROCESSING TIME is 2 TQ.
• SJW: (Re) Synchronization Jump Width is programmable between 1 and min(4, PHS1).
The total number of TQ in a bit time has to be programmed at least from 8 to 25.
Figure 16-7. Sample and Transmission Point
1
0
PD5
TXCAN
PD6
RXCAN
internal
TxCAN
internal
RxCAN
LISTEN
Bit Timing
Sample
Point
Transmission
Point
Prescaler BRP
PRS (3-bit length)
SJW (2-bit length)
PHS1 (3-bit length)
PHS2 (3-bit length)
CLK
IO
Fcan (Tscl)
Time Quantum
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