Datasheet

 1999-2013 Microchip Technology Inc. DS41106C-page 57
PIC16C712/716
FIGURE 9-8: EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 1
FIGURE 9-9: EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 2
FIGURE 9-10: EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 3
9.8 Time-out Sequence
On power-up the time-out sequence is as follows: First
PWRT time-out is invoked after the POR time delay has
expired. Then OST is activated. The total time-out will
vary based on oscillator configuration and the status of
the PWRT. For example, in RC mode with the PWRT
disabled, there will be no time-out at all. Figure 9-11,
Figure 9-12, and Figure 9-13 depict time-out
sequences on power-up.
Since the time-outs occur from the POR pulse, if MCLR
is kept low long enough, the time-outs will expire. Then
bringing MCLR
high will begin execution immediately
(Figure 9-13). This is useful for testing purposes or to
synchronize more than one PIC16CXXX device
operating in parallel.
Table 9-5 shows the Reset conditions for some Special
Function Registers, while Table 9-6 shows the Reset
conditions for all the registers.
Note 1: This circuit will activate Reset when
V
DD goes below (Vz + 0.7V) where
Vz = Zener voltage.
2: Internal Brown-out Reset circuitry
should be disabled when using this
circuit.
VDD
33k
10k
40k
V
DD
MCLR
PIC16C7XX
Q1
Note 1: This brown-out circuit is less expensive,
albeit less accurate. Transistor Q1 turns
off when VDD is below a certain level
such that:
2: Internal Brown-out Reset should be
disabled when using this circuit.
3: Resistors should be adjusted for the
characteristics of the transistor.
VDD x
R1
R1 + R2
= 0.7V
VDD
R2
40k
V
DD
MCLR
PIC16C7XX
R1
Q1
This brown-out protection circuit employs
Microchip Technology’s MCP809 microcontroller
supervisor. The MCP8XX and MCP1XX families
of supervisors provide push-pull and open
collector outputs with both high and low active
Reset pins. There are 7 different trip point
selections to accommodate 5V and 3V systems
MCLR
PIC16C7XX
VDD
VDD
Vss
RST
MCP809
VDD
bypass
capacitor