PIC17C42 Microchip Technology, PIC17C42 Datasheet - Page 18

• Manufacturer Part Number: PIC17C42
• Description: High-Performance 8-Bit CMOS EPROM/ROM Microcontroller
• Manufacturer: Microchip Technology

PIC17C4X
FIGURE 4-5:
FIGURE 4-6:
FIGURE 4-7:
DS30412C-page 18
This figure shows in greater detail the timings involved
with the oscillator start-up timer. In this example the
low frequency crystal start-up time is larger than
power-up time (T
Tosc1 = time for the crystal oscillator to react to an
oscillation level detectable by the Oscillator Start-up
Timer (ost).
T
INTERNAL RESET
PWRT TIME_OUT
This circuit will activate reset when V
(Vz + 0.7V) where Vz = Zener voltage.
OST
OST TIME_OUT
= 1024T
33k
V
OSC2
DD
MCLR
V
OSC
DD
OSCILLATOR START-UP TIME
PWRT
USING ON-CHIP POR
BROWN-OUT PROTECTION
CIRCUIT 1
10k
.
T
OSC
).
V
1
DD
40 k
T
PWRT
V
MCLR
MCLR
PIC17CXX
V
DD
PIC17CXX
DD
T
DD
OST
goes below
FIGURE 4-8:
FIGURE 4-9:
Note 1: An external Power-on Reset circuit is
This brown-out circuit is less expensive, albeit less
accurate. Transistor Q1 turns off when V
certain level such that:
V
2: R < 40 k is recommended to ensure
3: R1 = 100 to 1 k will limit any current
DD
R1
R2
D
V
required only if V
slow. The diode D helps discharge the
capacitor quickly when V
down.
that the voltage drop across R does not
exceed 0.2V (max. leakage current spec.
on the MCLR/V
voltage drop will degrade V
MCLR/V
flowing into MCLR from external capaci-
tor C in the event of MCLR/V
breakdown due to Electrostatic Dis-
charge (ESD) or (Electrical Overstress)
EOS.
DD
V
V
DD
DD
R
PIC17C42 EXTERNAL
POWER-ON RESET CIRCUIT
(FOR SLOW V
POWER-UP)
BROWN-OUT PROTECTION
CIRCUIT 2
C
PP
•
pin.
R1 + R2
R1
1996 Microchip Technology Inc.
Q1
PP
R1
40 k
DD
pin is 5 A). A larger
power-up time is too
MCLR
MCLR
PIC17C42
V
PIC17CXX
DD
= 0.7V
DD
DD
IH
powers
DD
PP
level on the
is below a
pin