When powering up any microcontroller it is necessary
for the power supply voltage to traverse voltage ranges,
where the device is not guaranteed to operate, before
the power supply voltage reaches its final state. Since
some circuits on the device (logic) will start operating at
voltage levels lower than other circuits on the chip
(memory), the device may power-up in an unknown
state. To guarantee that the device starts up in a known
state, it must contain a power-up reset circuit.
PIC16C5X microcontrollers are equipped with on-chip
Power-on Reset circuitry, which eliminates the need for
external reset logic. This circuit will function in most
power-up situations where V
DD
rise time is fast enough
(50 ms or less). This application note describes the typ-
ical power-up sequence for PIC16C5X
microcontrollers. Methods of assuring reset on
power-up and after a brown-out are discussed and sim-
ple, low-cost external solutions are discussed for
power-up situations where the PIC16C5X’s internal cir-
cuitry cannot provide the reset. AN522
Power-up Considerations
reset circuitry is shown in Figure 1. On power-up, the
Author: Sumit Mitra reset latch and the start-up timer are reset to appropri-
Microchip Technology Inc.
ate states by the Power-on Reset (POR). The start-up
timer will begin counting once it detects MCLR to be
high (i.e., external chip reset go……
