Datasheet

599
42023E–SAM–07/2013
ATSAM4L8/L4/L2
Figure 24-31. Slave Node Synchronization
The synchronization accuracy depends on:
• The theoretical slave node clock frequency; nominal clock frequency (F
Nom
)
• The baud rate
• The oversampling mode (OVER=0 => 16x, or OVER=1 => 8x)
The following formula is used to calculate synchronization deviation, where F
SLAVE
is the real
slave node clock frequency, and F
TOL_UNSYNC
is the difference between F
Nom
and F
SLAVE
. Accord-
ing to the LIN specification, F
TOL_UNSYNCH
may not exceed ±15%, and the bit rates between two
nodes must be within ±2% of each other, resulting in a maximal BaudRate_deviation of ±1%. If
F
TOL_UNSYNCH
exceeds ±15%, LINBRR will not be updated with new values, and the LIN Sync
Tolerance Error bit (CSR.LINSTE) is set.
Minimum nominal clock frequency with a fractional part:
Examples:
• Baud rate = 20 kbit/s, OVER=0 (Oversampling 16x) => F
Nom
(min) = 2.64MHz
• Baud rate = 20 kbit/s, OVER=1 (Oversampling 8x) => F
Nom
(min) = 1.47MHz
• Baud rate = 1 kbit/s, OVER=0 (Oversampling 16x) => F
Nom
(min) = 132 kHz
• Baud rate = 1 kbit/s, OVER=1 (Oversampling 8x) => F
Nom
(min) = 74 kHz
If the fractional part is not used, the synchronization accuracy is much lower. The 16 most signif-
icant bits, added with the first least significant bit, becomes the new clock divider (LINCD). The
equation of the baud rate deviation is the same as above, but the constants are:
RXD
Baud Rate
Clock
LINIDRX
Synchro Counter 000_0011_0001_0110_1101
BRGR
Clcok Divider (CD)
0000_0110_0010_1101
BRGR
Fractional Part (FP)
101
Initial CD
Initial FP
Reset
Start
Bit
10101010
Stop
Bit
Start
Bit
ID0 ID1 ID2 ID3 ID4 ID5 ID6 ID7Break 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×××
8F
SLAVE
×
---------------------------------------------------------------------------------------------------
×
⎝⎠
⎛⎞
%=
BaudRate_deviation 100
α[ 8 2 OVER–()β+ ] BaudRate×××
8
F
TOL_UNSYNC
100
------------------------------------
⎝⎠
⎛⎞
xF
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=