AT89C51CC03U-RDTIM datasheet(97/195 Pages) ATMEL

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AT89C51CC03

4182I–CAN–06/05

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 equal to the

INFORMATION PROCESSING TIME and inferior or equal to TPSH1.

•

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 51. Sample And Transmission Point

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

Tphs2 = Max of (Tphs1 and 2TQ)

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.

FCAN

CLOCK

Prescaler BRP

PRS 3-bit length

PHS1 3-bit length

PHS2 3-bit length

SJW 2-bit length

Bit Timing

System clock Tscl

Time Quantum

Sample point

Transmission point

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