AT89C51CC02CA-RATUM datasheet(85/156 Pages) ATMEL

85 / 156 page

AT/T89C51CC02

4126J–CAN–05/06

Figure 41. General Structure of a bit Period

example of bit timing determination for CAN baudrate of 500 kbit/s:

OSC

= 12 MHz in X1 mode => FCAN = 6MHz

Verify that the CAN baud rate you want is an integer division of FCAN clock.

FCAN/CANbaudrate = 6 MHz/500 kHz = 12

The time quanta TQ must be comprised between 8 and 25: TQ = 12 and BRP = 0

Define the various timing parameters: Tbit = Tsyns + Tprs + Tphs1 + Tphs2 =

12TQ

Tsyns = 1TQ and Tsjw =1TQ => SJW = 0

If we chose a sample point at 66.6% => Tphs2 = 4TQ => PHS2 = 3

Tbit = 12 = 4 + 1 + Tphs1 + Tprs, let us choose Tprs = 3 Tphs1 = 4

PHS1 = 3

and PRS = 2

BRP = 0 so CANBT1 = 00h

SJW = 0 and PRS = 2 so CANBT2 = 04h

PHS2 = 3 and PHS1 = 3 so CANBT3 = 36h

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)

AT89C51CC02CA-RATUM 数据表(PDF) 85 Page - ATMEL Corporation

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