PIC16F1933-ESLASHP datasheet(205/418 Pages) MICROCHIP

205 / 418 page

Preliminary

DS41364A-page 203

PIC16F193X/LF193X

19.6.3

START-UP CONSIDERATIONS

When any PWM mode is used, the application

hardware must use the proper external pull-up and/or

pull-down resistors on the PWM output pins.

The CCPxM<1:0> bits of the CCPxCON register 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 polarities

must be selected before the PWM pin output drivers are

enabled. Changing the polarity configuration while the

PWM pin output drivers are enable 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

initialized. Enabling the PWM pin output drivers at the

same time as the Enhanced PWM modes may cause

damage to the application circuit. The Enhanced PWM

modes must be enabled in the proper Output mode and

complete a full PWM cycle before enabling the PWM

pin output drivers. The completion of a full PWM cycle

is indicated by the TMRxIF bit of the PIRx register

being set as the second PWM period begins.

19.6.4

ENHANCED PWM

AUTO-SHUTDOWN MODE

The PWM mode supports an Auto-Shutdown mode that

will disable the PWM outputs when an external

shutdown event occurs. Auto-Shutdown mode places

the PWM output pins into a predetermined state. This

mode is used to help prevent the PWM from damaging

the application.

The auto-shutdown sources are selected using the

CCPxAS<2:0> bits of the CCPxAS register. A shutdown

event may be generated by:

•A logic ‘0’ on the INT pin

• Comparator Cx

• Setting the CCPxASE bit in firmware

A shutdown condition is indicated by the CCPxASE

(Auto-Shutdown Event Status) bit of the CCPxAS

normally. If the bit is a ‘1’, the PWM outputs are in the

shutdown state.

When a shutdown event occurs, two things happen:

The CCPxASE bit is set to ‘1’. The CCPxASE will

remain set until cleared in firmware or an auto-restart

occurs (see Section 19.6.5 “Auto-Restart Mode”).

The enabled PWM pins are asynchronously placed in

their shutdown states. The PWM output pins are

grouped into pairs [P1A/P1C] and [P1B/P1D]. The state

of each pin pair is determined by the PSSxAC and

PSSxBD bits of the CCPxAS register. Each pin pair may

be placed into one of three states:

• Drive logic ‘1’

• Drive logic ‘0’

• Tri-state (high-impedance)

Note:

When the microcontroller is released from

Reset, all of the I/O pins are in the

high-impedance state. The external cir-

cuits 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).

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