Atmel ARM-Based Evaluation Kit AT91SAM9N12-EK AT91SAM9N12-EK Data Sheet

789

SAM9N12/SAM9CN11/SAM9CN12 [DATASHEET]

11063K–ATARM–05-Nov-13

The accuracy of the synchronization depends on several parameters:



The nominal clock frequency (f

Nom

) (the theoretical slave node clock frequency)



The Baud Rate



The oversampling (Over=0 => 16X or Over=0 => 8X)

The following formula is used to compute the deviation of the slave bit rate relative to the master bit rate after
synchronization (f

SLAVE

 is the real slave node clock frequency).

f

TOL_UNSYNCH

 is the deviation of the real slave node clock from the nominal clock frequency. The LIN Standard imposes

that it must not exceed ±15%. The LIN Standard imposes also that for communication between two nodes, their bit rate
must not differ by more than ±2%. This means that the baudrate_deviation must not exceed ±1%.

It follows from that, a minimum value for the nominal clock frequency:

Examples:



Baud rate = 20 Kb/s, OVER=0 (Oversampling 16X) => f

Nom

(min) = 2.64 MHz



Baud rate = 20 Kb/s, OVER=1 (Oversampling 8X) => f

Nom

(min) = 1.47 MHz



Baud rate = 1 Kb/s, OVER=0 (Oversampling 16X) => f

Nom

(min) = 132 kHz



Baud rate = 1 Kb/s, OVER=1 (Oversampling 8X) => f

Nom

(min) = 74 kHz

 

 

 

RXD

Baud Rate

 Clock

LINIDRX

Synchro Counter

000_0011_0001_0110_1101

US_BRGR

Clcok Divider (CD)

US_BRGR

Fractional Part (FP)

Initial CD

Initial FP

Reset

 

 

US_LINBRR

Clcok Divider (CD)

0000_0110_0010_1101

US_LINBRR

Fractional Part (FP)

101

Initial CD

Initial FP

Start

Bit

1

0

1

0

1

0

1

0

Stop

Bit

Start

Bit

ID0 ID1 ID2 ID3 ID4 ID5 ID6 ID7

Break Field

13 dominant bits (at 0)

Stop

Bit

Break

Delimiter

1 recessive bit

(at 1)

Synch Byte = 0x55

Baudrate_deviation

100

α

[

8

2

Over

–

(

) β

+

]

Baudrate

×

×

×

8

f

SLAVE

×

---------------------------------------------------------------------------------------------

×









%

=

Baudrate_deviation

100

α

[

8

2

Over

–

(

) β

+

]

Baudrate

×

×

×

8

f

TOL_UNSYNCH

100

-------------------------------------









 f

Nom

×

×

---------------------------------------------------------------------------------------------

×





















%

=

0.5

–

α

+0.5    -1

β

+1

< <

≤ ≤

f

Nom

min

(

)

100

0.5

8

2

Over

–

(

)

×

×

1

+

[

]

Baudrate

×

8

15

–

100

----------

1

+









×

1%

×

------------------------------------------------------------------------------------------------

×





















Hz

=