PIC16C56A Microchip Technology Inc., PIC16C56A Datasheet - Page 25

• Manufacturer Part Number: PIC16C56A
• Description: Eprom/rom-based 8-bit Cmos Microcontroller Series
• Manufacturer: Microchip Technology Inc.

5.2
The Device Reset Timer (DRT) provides an 18 ms
nominal time-out on RESET regardless of Oscillator
mode used. The DRT operates on an internal RC oscil-
lator. The processor is kept in RESET as long as the
DRT is active. The DRT delay allows V
V
Oscillator circuits based on crystals or ceramic resona-
tors require a certain time after power-up to establish a
stable oscillation. The on-chip DRT keeps the device in
a RESET condition for approximately 18 ms after the
voltage on the MCLR/V
(V
the MCLR input are not required in most cases, allow-
ing for savings in cost-sensitive and/or space restricted
applications.
The Device Reset time delay will vary from chip to chip
due to V
AC parameters for details.
The DRT will also be triggered upon a Watchdog Timer
time-out. This is particularly important for applications
using the WDT to wake the PIC16C5X from SLEEP
mode automatically.
5.3
A brown-out is a condition where device power (V
dips below its minimum value, but not to zero, and then
recovers. The device should be RESET in the event of
a brown-out.
To RESET PIC16C5X devices when a brown-out
occurs, external brown-out protection circuits may be
built, as shown in Figure 5-6, Figure 5-7 and Figure 5-
8.
FIGURE 5-6:
This circuit will activate RESET when V
+ 0.7V (where Vz = Zener voltage).
DD
IH
2002 Microchip Technology Inc.
) level. Thus, external RC networks connected to
min., and for the oscillator to stabilize.
33K
V
DD
Device Reset Timer (DRT)
Reset on Brown-Out
DD
, temperature, and process variation. See
10K
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 1
PP
Q1
40K
pin has reached a logic high
MCLR
PIC16C5X
V
DD
DD
DD
goes below Vz
to rise above
Preliminary
DD
)
FIGURE 5-7:
FIGURE 5-8:
This brown-out circuit is less expensive, although
less accurate. Transistor Q1 turns off when V
is below a certain level such that:
This brown-out protection circuit employs Micro-
chip
supervisor. The MCP8XX and MCP1XX families
of supervisors provide push-pull and open collec-
tor outputs with both "active high and active low"
RESET pins. There are 7 different trip point selec-
tions to accommodate 5V and 3V systems.
Vss
MCP809
V
Technology’s
DD
R1
R2
V
DD
RST
V
DD
V
DD
•
capacitor
bypass
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 2
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 3
R1 + R2
MCP809
R1
PIC16C5X
Q1
40K
= 0.7V
PIC16C5X
MCLR
PIC16C5X
V
MCLR
V
DS30453D-page 23
DD
DD
microcontroller
DD