PIC16F636T-I/SL(2005) View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

PIC16F636T-I/SL
(Rev.:2005)

8/14-Pin Flash-Based, 8-Bit CMOS Microcontrollers with nanoWatt Technology

Microchip Technology 

PIC12F635/PIC16F636/639

12.3 Power-on Reset

The on-chip POR circuit holds the chip in Reset until VDD

has reached a high enough level for proper operation. To

take advantage of the POR, simply connect the MCLR

pin through a resistor to VDD. This will eliminate external

RC components usually needed to create Power-on

Reset. A maximum rise time for VDD is required. See

Section 15.0 “Electrical Specifications” for details. If

the BOD is enabled, the maximum rise time specification

does not apply. The BOD circuitry will keep the device in

Reset until VDD reaches VBOD (see Section 12.6

“Brown-out Detect (BOD)”).

Note:

The POR circuit does not produce an

internal Reset when VDD declines. To

re-enable the POR, VDD must reach VSS

for a minimum of 100 μs.

When the device starts normal operation (exits the

Reset condition), device operating parameters (i.e.,

voltage, frequency, temperature, etc.) must be met to

ensure operation. If these conditions are not met, the

device must be held in Reset until the operating

conditions are met.

For additional information, refer to the Application Note

AN607, “Power-up Trouble Shooting” (DS00607).

12.4 Wake-up Reset (WUR)

The PIC12F635/PIC16F636/639 has a modified wake-

up from Sleep mechanism. When waking from Sleep,

the WUR function resets the device and releases Reset

when VDD reaches an acceptable level.

If the WURE bit is enabled (‘0’) in the Configuration

Word register, the device will Wake-up Reset from

Sleep through one of the following events:

1. On any event that causes a wake-up event. The

peripheral must be enabled to generate an

interrupt or wake-up, GIE state is ignored.

2. When WURE is enabled, RA3 will always

generate an interrupt-on-change signal during

Sleep.

The WUR, POR and BOD bits in the PCON register

and the TO and PD bits in the Status register can be

used to determine the cause of device Reset.

To allow WUR upon RA3 change:

1. Enable the WUR function, WURE Configuration

Bit = 0.

2. Enable RA3 as an input, MCLRE Configuration

Bit = 0.

3. Read PORTA to establish the current state of

RA3.

4. Execute SLEEP instruction.

5. When RA3 changes state, the device will wake-

up and then reset. The WUR bit in PCON will be

cleared to ‘0’.

12.5 MCLR

PIC12F635/PIC16F636/639 has a noise filter in the

MCLR Reset path. The filter will ignore small pulses.

It should be noted that a WDT Reset does not drive

MCLR pin low. See Figure 12-2 for the recommended

MCLR circuit.

An internal MCLR option is enabled by clearing the

MCLRE bit in the Configuration Word register. When

cleared, MCLR is internally tied to VDD and an internal

weak pull-up is enabled for the MCLR pin. In-Circuit

Serial Programming is not affected by selecting the

internal MCLR option.

FIGURE 12-2:

RECOMMENDED MCLR

CIRCUIT

VDD

R1

1 kΩ (or greater)

PIC12F635/PIC16F636/639

MCLR

C1

0.1 μF

(optional, not critical)

DS41232B-page 114

Preliminary

© 2005 Microchip Technology Inc.

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