MPC5553/MPC5554 Microcontroller Reference Manual, Rev. 5
Freescale Semiconductor 17-31
to indicate the start and end points of a complete period have been captured. This sequence of events is
repeated for each subsequent capture. Registers EMIOS_CADRn and EMIOS_CBDRn return the values
in register A2 and B1, respectively.
In order to guarantee coherent access, reading EMIOS_CADRn disables transfers between B2 and B1 until
reading EMIOS_CBDRn register, then any pending transfer is re-enabled.
The input pulse period is calculated by subtracting the value in B1 from A2.
Figure 17-19 shows how the unified channel can be used for input period measurement.
Figure 17-19. Input Period Measurement Example
17.4.4.4.6 Double Action Output Compare Mode (DAOC)
In the DAOC mode the leading and trailing edges of the variable pulse width output are generated by
matches occurring on comparators A and B, respectively.
When the DAOC mode is first selected (coming from GPIO mode) both comparators are disabled.
Comparators A and B are enabled by updating registers A1 and B1 respectively and remain enabled until
a match occurs on that comparator, when it is disabled again. In order to update registers A1 and B1, a
write to A2 and B2 must occur and the EMIOS_CCRn[ODIS] bit must be cleared.
The output flip-flop is set to the value of EMIOS_CCRn[EDPOL] when a match occurs on comparator A
and to the complement of EDPOL when a match occurs on comparator B.
MODE[6] controls if the EMIOS_CSRn[FLAG] is set on both matches or just on the second match (see
Table 17-11 for details).
If subsequent enabled output compares occur on registers A1 and B1, pulses will continue to be generated,
regardless of the state of the FLAG bit.
Table 17-19. Mode of Operation: DAOC Mode
MODE[0:6] Unified Channel Mode of Operation
0b0000110 Double action output compare (with FLAG set on the second match)
0b0000111 Double action output compare (with FLAG set on both match)
0x000500 0x001000 0x001100 0x001250 0x001525 0x0016A0
Selected
Counter Bus
FLAG
Set Event
AAA
Captured A2
Val ue
2
0xxxxxxx 0x001000 0x0016A0
Notes:
1
After input filter.
2
Reading EMIOS_CADRn returns the value of A2, writing EMIOS_CADRn writes to A2.
Input Signal
1
EDPOL = 1
B1 Value
3
0x001250
0xxxxxxx 0xxxxxxx 0x0012500x001000
0xxxxxxx 0x001000 0x0016A00x001250
Captured B2
Val ue
3
Reading EMIOS_CBDRn returns the value of B1, writing EMIOS_CBDRn writes to B1.
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