586
SAM9G45 [DATASHEET]
6438K–ATARM–12-Feb-13
The following formula is used to compute the deviation of the slave bit rate relative to the master bit rate after syn-
chronization (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:
Baudrate = 20 kbit/s, Over=0 (Oversampling 16X) => F
Nom(min) = 2.64 MHz
Baudrate = 20 kbit/s, Over=1 (Oversampling 8X) => F
Nom(min) = 1.47 MHz
Baudrate = 1 kbit/s, Over=0 (Oversampling 16X) => F
Nom(min) = 132 kHz
Baudrate = 1 kbit/s, Over=1 (Oversampling 8X) => F
Nom(min) = 74 kHz
If the fractional baud rate is not used, the accuracy of the synchronization becomes much lower. When the counter
is stopped, the 16 most significant bits of the counter (value divided by 8) gives the new clock divider (CD). This
value is rounded by adding the first insignificant bit. The equation of the Baudrate deviation is the same as given
above, but the constants are as follows:
It follows from that, a minimum value for the nominal
clock frequency:
Examples:
Baudrate = 20 kbit/s, Over=0 (Oversampling 16X) => F
Nom(min) = 19.12 MHz
Baudrate = 20 kbit/s, Over=1 (Oversampling 8X) => F
Nom(min) = 9.71 MHz
Baudrate = 1 kbit/s, Over=0 (Oversampling 16X) => F
Nom(min) = 956 kHz
Baudrate = 1 kbit/s, Over=1 (Oversampling 8X) => F
Nom(min) = 485 kHz
Baudrate_deviation
100
α
[
8
2
Over
–
() β
+
] Baudrate
×
8F
SLAVE
×
--------------------------------------------------------------------------------------------
×
%
=
Baudrate_deviation
100
α
[
8
2
Over
–
() β
+
] Baudrate
×
8
F
TOL_UNSYNCH
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
=
4
–
α +4
-1
β +1
<<
≤≤
F
NOM
(min)
100
4
8
2
Over
–
()
×
1
+
[] Baudrate
×
8
15
–
100
----------
1
+
×
1%
×
-------------------------------------------------------------------------------------------
×
Hz
=