PIC16F753 datasheet(89/230 Pages) MICROCHIP

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DS40001709C-page 89

PIC16F753/HV753

11.8

Auto-shutdown Control

Auto-shutdown is a method to immediately override

the COG output levels with specific overrides that

allow for safe shutdown of the circuit.

The

shutdown

state

can

either

cleared

automatically or held until cleared by software. In

either case, the shutdown overrides remain in effect

until the first rising event after the shutdown is cleared.

11.8.1

SHUTDOWN

The shutdown state can be entered by either of the

following two mechanisms:

• Software generated

• External Input

11.8.1.1

Software Generated Shutdown

Setting the GxASDE bit of the COGxASD0 register

(Register 11-7) will force the COG into the shutdown

state.

When auto-restart is disabled, the shutdown state will

persist until the first rising event after the GxASDE bit

is cleared by software.

When auto-restart is enabled, the GxASDE bit will

clear automatically and resume operation on the first

rising event after the shutdown input clears. See

Figure 11-8 and Section 11.8.3.2 “Auto-Restart”.

11.8.1.2

External Shutdown Source

External shutdown inputs provide the fastest way to

safely suspend COG operation in the event of a Fault

condition. When any of the selected shutdown inputs

goes true, the output drive latches are reset and the

COG outputs immediately go to the selected override

levels without software delay.

Any combination of the input sources can be selected

to cause a shutdown condition. Shutdown input

sources include:

• HLTimer1 output

• HLTimer2 output

• C2OUT (low true)

• C1OUT (low true)

• COG1FLT pin (low true)

Shutdown inputs are selected independently with bits

of the COGxASD1 register (Register 11-8).

11.8.2

PIN OVERRIDE LEVELS

The levels driven to the output pins, while the

shutdown

active,

are

controlled

the

GxASD0L<1:0> and GxASD1L<1:0> bits

of the

COGxASD0 register (Register 11-7). GxASD0L<1:0>

controls

the

GxOUT0

override

level

and

GxASD1L<1:0> controls the GxOUT1 override level.

There are four override options for each output:

•Forced low

• Forced high

• Tri-state

• PWM inactive state (same state as that caused by

a falling event)

11.8.3

AUTO-SHUTDOWN RESTART

After an auto-shutdown event has occurred, there are

two ways to have the module resume operation:

• Software controlled

• Auto-restart

The restart method is selected with the GxARSEN bit

of the COGxASD0 register. Waveforms of a software

controlled automatic restart are shown in Figure 11-8.

11.8.3.1

Software Controlled Restart

When the GxARSEN bit of the COGxASD0 register is

cleared, software must clear the GxASDE bit to restart

COG operation after an auto-shutdown event.

The COG will resume operation on the first rising

event after the GxASDE bit is cleared. Clearing the

shutdown state requires all selected shutdown inputs

to be false, otherwise, the GxASDE bit will remain set.

11.8.3.2

Auto-Restart

When the GxARSEN bit of the COGxASD0 register is

set, the COG will restart from the auto-shutdown state

automatically.

The GxASDE bit will clear automatically and the COG

will resume operation on the first rising event after all

selected shutdown inputs go false.

Note:

Shutdown inputs are level-sensitive, not

edge-sensitive.

The

shutdown

state

cannot

cleared

long

the

shutdown input level persists, except by

disabling auto-shutdown.

Note:

The polarity control does not apply to the

forced low and high override levels.

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