Information

Set EXSPC
Clear EXSPC
Figure 40-19. Extended space operation
40.7.4.2 EXSPC operation in FSK mode
In FSK mode, the modulator continues to count carrier out clocks, alternating between
the primary and secondary registers at the end of each modulation period.
To calculate the length of an extended space in FSK mode, it is required to know whether
MSC[EXSPC] was set on a primary or secondary modulation period, and the total
number of both primary and secondary modulation periods completed while
MSC[EXSPC] is high. A status bit for the current modulation is not accessible to the
CPU. If necessary, software must maintain tracking of the current primary or secondary
modulation cycle. The extended space period ends at the completion of the space period
time of the modulation period during which MSC[EXSPC]is cleared.
The following table depicts the equations which can be used to calculate the extended
space period depending on when MSC[EXSPC] is set.
If Then
MSC[EXSPC] was set during a primary
modulation cycle
Use the equation:
t
exspace
= (t
space
)
p
+ (t
mark
+ t
space
)
s
+ (t
mark
+ t
space
)
p
+...
MSC[EXSPC] bit was set during a secondary
modulation cycle
Use the equation:
t
exspace
= (t
space
)
s
+ (t
mark
+ t
space
)
p
+ (t
mark
+ t
space
)
s
+...
Where the subscripts p and s refer to mark and space times for the primary and secondary
modulation cycles.
Functional description
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
1008
Preliminary
Freescale Semiconductor, Inc.
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