2012 Microchip Technology Inc. DS01450A-page 1
AN1450
INTRODUCTION
In this application note, a PIC10F322 is being used to
implement a delay block/debouncer. The delay can be
set between 2 µs and 193 µs. This can be used
effectively as a noise discriminator, or for switch
debouncing.
When used as a delay block, the application can be
used to fix low-level timing issues on signals. When
used as a debouncer, it can debounce signals from a
mechanical switch so that a clean signal can feed other
circuitry.
The application makes use of the Configurable Logic
Cell (CLC) peripheral to produce fast switching on the
output (if desired). If the same application were written
using port logic only, there would be multiple instruction
cycles before the output would change in response to
an input. Using the CLC the signal can be routed
directly and only have propagation and gate delay
between the input and output signals. In order to get
the highest performance possible from the application,
it has been written in assembly.
The code has been written in-line (without subroutines)
to maximize switching performance of the application.
The code uses only 43 locations of program memory
(512 available), and one byte of RAM.
This application note was developed using a
PIC10F322 demo board (part # AC103011). Language
tool versions: MPASMWIN.exe v5.45, mplink.exe
v4.43, mplib.exe v4.43.
DELAY SETTINGS AND VALUES
Delays can be set between 2 µs and 193 µs in 750 ns
increments (using the 16 MHz internal clock). Delays
can easily be made longer if desired, by reducing the
clock speed or increasing the size of the delay loop.
Enabling/disabling of delays is configured in the code
by commenting/uncommenting the following lines of
code:
Independent rising and falling edge delay times can be
set in the following lines of code:
Voltage: 2.3 to 5.5V.
CALCULATING DELAY VALUES
There are two options for setting delay values, and they
are determined by commenting/uncommenting the
MS_DELAY definition:
1. 1 millisecond step size – this is useful for switch
debouncing with recommended settings of
FALLING_EDGE_DELAY = 100 ms, and
RISING_EDGE_DELAY disabled.
Delays are set in milliseconds.
2. 750 ns step size
With the part running at 16 MHz, there are 250 ns per
instruction cycle. The delay loop takes three instruction
cycles to execute, so 750 ns are added for each
incremental change in the countdown timer. There are
approximately eight instructions (2 µs) that will be
executed between an input change and an output
change, if the shortest possible delay is selected
(RISING_EDGE_DELAY or FALLING_EDGE_DELAY
= 1).
Operating current: ~ 2.4 mA (but can be reduced with
lower clock speed).
MODES OF OPERATION
Rising Edge Delay
In this mode, only the rising edge has a delay, and the
falling edge will drop immediately.
Author: Stephen Allen
Microchip Technology Inc.
;; 2 lines below enable rising and falling
edge delays
#define RISING_EDGE_DELAY
#define FALLING_EDGE_DELAY
;; specify length of falling and rising edge
below
RISE_EDGE_DELAY equ 0x01
FALL_EDGE_DELAY equ 0x01
#define MS_DELAY
;#define MS_DELAY
delay = 2 µs + (delay_value x 750 ns)
Delay Block/Debouncer
剩余13页未读，继续阅读
资源评论
