T89C51CC01 Atmel, T89C51CC01 Datasheet - Page 90

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

Bit Timing and Baud Rate
Figure 47. Sample And Transmission Point
90
T89C51CC01
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:
•
•
•
•
•
•
•
•
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 equal 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 3-bit length
PHS1 3-bit length
PHS2 3-bit length
SJW 2-bit length
Bit Timing
Sample point
Transmission point
4129K–CAN–01/05