Information

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.
38.8 CMT interrupts and DMA
The CMT generates an interrupt request or a DMA transfer request according to
MSC[EOCIE], MSC[EOCF], DMA[DMA] bits.
Table 38-23. DMA transfer request x CMT interrupt request
MSC[EOCF] DMA[DMA] MSC[EOCIE] DMA transfer request CMT interrupt request
0 X X 0 0
1 X 0 0 0
1 0 1 0 1
1 1 1 1 0
MSC[EOCF] is set:
• When the modulator is not currently active and MSC[MCGEN] is set to begin the
initial CMT transmission.
• At the end of each modulation cycle when the counter is reloaded from
CMD1:CMD2, while MSC[MCGEN] is set.
When MSC[MCGEN] is cleared and then set before the end of the modulation cycle,
MSC[EOCF] will not be set when MSC[MCGEN] is set, but will become set at the end
of the current modulation cycle.
Chapter 38 Carrier Modulator Transmitter (CMT)
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
Freescale Semiconductor, Inc. 863