AT89C51CC02CA-RATUM datasheet(84/156 Pages) ATMEL

84 / 156 page

AT/T89C51CC02

4126J–CAN–05/06

Bit Timing and Baud

Rate

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 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.

The total number of TQ in a bit time has to be programmed at least from 8 to 25.

Figure 40. Sample and Transmission Point

The baud rate selection is made by Tbit calculation:

Tbit = Tsyns + Tprs + Tphs1 + Tphs2

Tsyns = Tscl = (BRP[5..0]+ 1)/Fcan = 1TQ

Tprs = (1 to 8) * Tscl = (PRS[2..0]+ 1) * Tscl

Tphs1 = (1 to 8) * Tscl = (PHS1[2..0]+ 1) * Tscl

Tphs2 = (1 to 8) * Tscl = (PHS2[2..0]+ 1) * Tscl

Tphs2 = Max of (Tphs1 and 2TQ)

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.

FCAN

CLOCK

Prescaler BRP

PRS 3bit length

PHS1 3bit length

PHS2 3bit length

SJW 2-bit length

bit Timing

System Clock Tscl

Time Quantum

Sample Point

Transmission Point

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