Enhanced Modular Input/Output Subsystem (eMIOS200)
23-58
Freescale Semiconductor
PXR40 Microcontroller Reference Manual, Rev. 1
Figure 23-52. OPWM with Next Period Update
23.4.1.1.18
Output Pulse-Width Modulation Buffered (OPWMB) Mode
OPWMB mode (MODE = 110_00b0) is used to generate pulses with programmable leading- and
trailing-edge placement. An external counter must be selected from one of the counter buses. The A1
register value defines the first edge and B1 defines the second edge. The output signal polarity is defined
by the EDPOL bit. If EDPOL is 0, a negative edge occurs when A1 matches the selected counter bus; and
a positive edge occurs when B1 matches the selected counter bus.
The A1 and B1 registers are double buffered and updated from A2 and B2, respectively, at the cycle
boundary. The load operation is similar to the OPWFMB mode. Please refer to
for more
information about A1 and B1 registers update.
FLAG can be generated at B1 matches, when MODE[5] is cleared, or in both A1 and B1 matches, when
MODE[5] is set. If subsequent matches occur on comparators A and B, the PWM pulses continue to be
generated, regardless of the state of the FLAG bit.
FORCMA and FORCMB bits allow the software to force the output flip-flop to the level corresponding
to a match on A1 or B1 respectively. The FLAG bit is not set by the FORCMA and FORCMB operations.
At OPWMB mode entry the output flip-flop is set to the value of the EDPOL bit in the EMIOS_CCR[
n
]
register.
Some rules applicable to the OPWMB mode include:
•
B1 matches have precedence over A1 matches if they occur at the same time within the same
counter cycle
•
A1 = 0 match from cycle(
n
) has precedence over B1 match from cycle(
n
– 1)
•
A1 matches are masked out if they occur after B1 match within the same cycle
0x
FFFFFF
0x
001000
0x
000000
Selected Counter Bus
Time
Output Flip-Flop
A1 Value
1
0x
000200
B1 Value
B2 Value
2
0x000200
0x000900
0xxxxxxx
0x000200
0x001000
0x
000900
0x001000
Notes: 1. EMIOS_CADR[n] = A1
2. EMIOS_CBDR[n] = B2
0x001000
0x000900
0x000900
A2 = A1 and A2 = A1 according to OU[n] bit
MODE[6] = 1
A1 Match
A1 & B2
Write
B1 Match
B2
Write
A1 Match
B1 Match
Summary of Contents for PXR4030
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