PIC16F684-ESLASHST datasheet(89/164 Pages) MICROCHIP

89 / 164 page

 2004 Microchip Technology Inc.

Preliminary

DS41202C-page 87

PIC16F684

11.3.7.1

Auto-shutdown and Auto-restart

The auto-shutdown feature can be configured to allow

auto-restarts of the module following a shutdown event.

This is enabled by setting the PRSEN bit of the

PWM1CON register (PWM1CON<7>).

In Shutdown mode with PRSEN = 1 (Figure 11-12), the

ECCPASE bit will remain set for as long as the cause

of the shutdown continues. When the shutdown condi-

tion clears, the ECCPASE bit is cleared. If PRSEN = 0

(Figure 11-13), once a shutdown condition occurs, the

ECCPASE bit will remain set until it is cleared by firm-

ware. Once ECCPASE is cleared, the enhanced PWM

will resume at the beginning of the next PWM period.

Independent of the PRSEN bit setting, whether the

auto-shutdown source is one of the comparators or

INT, the shutdown condition is a level. The ECCPASE

bit cannot be cleared as long as the cause of the shut-

down persists.

The Auto-shutdown mode can be forced by writing a ‘1’

to the ECCPASE bit.

11.3.8

START-UP CONSIDERATIONS

When the ECCP module is used in the PWM mode, the

application hardware must use the proper external

pull-up and/or pull-down resistors on the PWM output

pins. When the microcontroller is released from Reset,

all of the I/O pins are in the high-impedance state. The

external circuits must keep the power switch devices in

the off state, until the microcontroller drives the I/O pins

with the proper signal levels, or activates the PWM

output(s).

The CCP1M<1:0> bits (CCP1CON<1:0>) allow the

user to choose whether the PWM output signals are

active-high or active-low for each pair of PWM output

pins (P1A/P1C and P1B/P1D). The PWM output polar-

ities must be selected before the PWM pins are config-

ured as outputs. Changing the polarity configuration

while the PWM pins are configured as outputs is not

recommended since it may result in damage to the

application circuits.

The P1A, P1B, P1C and P1D output latches may not

be in the proper states when the PWM module is initial-

ized. Enabling the PWM pins for output at the same

time as the ECCP module may cause damage to the

application circuit. The ECCP module must be enabled

in the proper Output mode and complete a full PWM

cycle before configuring the PWM pins as outputs. The

completion of a full PWM cycle is indicated by the

TMR2IF bit being set as the second PWM period

begins.

FIGURE 11-12:

PWM AUTO-SHUTDOWN (PRSEN = 1, AUTO-RESTART ENABLED)

FIGURE 11-13:

PWM AUTO-SHUTDOWN (PRSEN = 0, AUTO-RESTART DISABLED)

Note:

Writing to the ECCPASE bit is disabled

while a shutdown condition is active.

Shutdown

PWM

ECCPASE bit

Activity

Event

Shutdown

Event Occurs

Shutdown

Event Clears

PWM

Resumes

Normal PWM

Start of

PWM Period

Shutdown

PWM

ECCPASE bit

Activity

Event

Shutdown

Event Occurs

Shutdown

Event Clears

PWM

Resumes

Normal PWM

Start of

PWM Period

ECCPASE

Cleared by

Firmware

PWM Period

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