Rainbow Electronics T89C51CC02 - Manual (Page 74)

74 Rev.A - May 17, 2001
Preliminary
T89C51CC02
15.5. Bit Timing and BaudRate
The baud rate selection is made by Tbit calculation:
Tbit = Tsyns + Tprs + Tphs1 + Tphs2
1. Tsyns = Tscl = (BRP[5..0]+ 1) / Fcan.
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 is from 8 to 25.
Figure 60. General structure of a bit period
example:
For a Baud Rate of 100 kbit/s and Fosc = 12 MHz For have 10 TQ:
BRP = 5
PRS = 2
PHS2 = 2
PHS1 = 2
Bit Rate Prescaler
oscillator
1/ Fcan
Tscl
system clock
one nominal bit
Tsyns (*) Tprs
Sample Point
(*) Synchronization Segment: SYNS
Tbit
Tsyns = 1xTscl (fixed)
data
Tbit Tsyns Tprs Tphs1 Tphs2 + + + = Tbit calculation:
Transmission Point
Tphs1 + Tsjw (3)
Tphs2 - Tsjw (4)
(1) Phase error
≤
0
(2) Phase error
≥
0
(3)
Phase error > 0
(4)
Phase error < 0
Tphs2 (2)
Tphs1 (1)