AT89C51CC02CA-TDSUM ATMEL [ATMEL Corporation], AT89C51CC02CA-TDSUM Datasheet - Page 84

• Manufacturer Part Number: AT89C51CC02CA-TDSUM
• Description: Enhanced 8-bit Microcontroller with CAN Controller and Flash
• Manufacturer: ATMEL [ATMEL Corporation]

Bit Timing and Baud
Rate
Figure 40. Sample and Transmission Point
84
AT/T89C51CC02
CLOCK
FCAN
Prescaler BRP
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:
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The total number of TQ in a bit time has to be programmed at least from 8 to 25.
The baud rate selection is made by Tbit calculation:
Tbit = Tsyns + Tprs + Tphs1 + Tphs2
1. Tsyns = Tscl = (BRP[5..0]+ 1)/Fcan = 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]+ 1) * Tscl
5. Tsjw = (1 to 4) * Tscl = (SJW[1..0]+ 1) * Tscl
The total number of Tscl (Time Quanta) in a bit time must be comprised between 8 to
25.
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 superior or eual to the Information
Processing Time and inferior or equal to TPHS1
INFORMATION PROCESSING TIME is 2 TQ.
SJW: (Re) Synchronization Jump Width is programmable to be minimum of PHS1
and 4.
Tphs2 = Max of (Tphs1 and 2TQ)
System Clock Tscl
Time Quantum
PRS 3bit length
PHS1 3bit length
PHS2 3bit length
SJW 2-bit length
bit Timing
Sample Point
Transmission Point
4126J–CAN–05/06