PIC18LF4331-ESLASHML datasheet(194/392 Pages) MICROCHIP

194 / 392 page

PIC18F2331/2431/4331/4431

DS39616D-page 194

 2010 Microchip Technology Inc.

18.8.2

PWM CHANNEL OVERRIDE

PWM output may be manually overridden for each

PWM channel by using the appropriate bits in the

OVDCOND and OVDCONS registers. The user may

select the following signal output options for each PWM

output pin operating in the Independent PWM mode:

• I/O pin outputs PWM signal

• I/O pin inactive

• I/O pin active

Refer to Section 18.10 “PWM Output Override” for

details for all the override functions.

FIGURE 18-19:

CENTER CONNECTED

LOAD

18.9

Single-Pulse PWM Operation

The single-pulse PWM operation is available only in

Edge-Aligned mode. In this mode, the PWM module

will

produce

single-pulse

output.

Single-pulse

operation is configured when the PTMOD<1:0> bits are

set to ‘01’ in the PTCON0 register. This mode of

operation is useful for driving certain types of ECMs.

In Single-Pulse mode, the PWM I/O pin(s) are driven to

the active state when the PTEN bit is set. When the

PWM timer match with the Duty Cycle register occurs,

the PWM I/O pin is driven to the inactive state. When

the PWM timer match with the PTPER register occurs,

the PTMR register is cleared, all active PWM I/O pins

are driven to the inactive state, the PTEN bit is cleared

and an interrupt is generated if the corresponding

interrupt bit is set.

18.10 PWM Output Override

The PWM output override bits allow the user to manu-

ally drive the PWM I/O pins to specified logic states,

independent of the duty cycle comparison units. The

PWM override bits are useful when controlling various

types of ECMs like a BLDC motor.

OVDCOND and OVDCONS registers are used to

define the PWM override options. The OVDCOND

contains

eight

bits,

POVD<7:0>,

that

determine which PWM I/O pins will be overridden. The

OVDCONS register contains eight bits, POUT<7:0>,

that determine the state of the PWM I/O pins when a

particular output is overridden via the POVD bits.

The POVD bits are active-low control bits. When the

POVD bits are set, the corresponding POUT bit will

have no effect on the PWM output. In other words, the

pins corresponding to POVD bits that are set will have

the duty PWM cycle set by the PDCx registers. When

one of the POVD bits is cleared, the output on the cor-

responding PWM I/O pin will be determined by the

state of the POUT bit. When a POUT bit is set, the

PWM pin will be driven to its active state. When the

POUT bit is cleared, the PWM pin will be driven to its

inactive state.

18.10.1

COMPLEMENTARY OUTPUT MODE

The even numbered PWM I/O pins have override

restrictions when a pair of PWM I/O pins are operating

in the Complementary mode (PMODx = 0). In Comple-

mentary mode, if the even numbered pin is driven

active by clearing the corresponding POVD bit and by

setting POUT bits in the OVDCOND and OVDCONS

registers, the output signal is forced to be the comple-

ment of the odd numbered I/O pin in the pair (see

Figure 18-2 for details).

18.10.2

OVERRIDE SYNCHRONIZATION

If the OSYNC bit in the PWMCON1 register is set, all

output overrides performed via the OVDCOND and

OVDCONS registers will be synchronized to the PWM

time base. Synchronous output overrides will occur on

the following conditions:

• When the PWM is in Edge-Aligned mode,

synchronization occurs when PTMR is zero.

• When the PWM is in Center-Aligned mode,

synchronization occurs when PTMR is zero and

when the value of PTMR matches PTPER.

Note:

PTPER and PDCx values are held as they

are after the single-pulse output. To have

another cycle of single pulse, only PTEN

has to be enabled.

PWM1

PWM0

Load

Note 1:

In the Complementary mode, the even

channel cannot be forced active by a

Fault or override event when the odd

channel is active. The even channel is

always the complement of the odd

channel with dead time inserted, before

the odd channel can be driven to its

active state, as shown in Figure 18-20.

Dead time is inserted in the PWM

channels even when they are in Override

mode.

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