Project
description:
In this project, 8 LEDs are connected to
PORT B of a PIC microcontroller. Also a push-button switch is connected to bit 0
of PORT A using a pull-up resistor.. When the switch is pressed the LEDs scroll
to the right.
Hardware:
The
circuit diagram of the project is shown in Figure 1. The circuit in this
project additionally a switch is connected to bit 0 of PORTA to control the
direction of scrolling. A PIC16F627 model PIC micro controller is used and the micro controller
is operated from its 4 MHz internal clock. The LEDs are connected to 8 pins of
PORT B using 330_ current-limiting resistors. An external reset button is
connected to MCLR input of the microcontroller.
Figure
1 Circuit
diagram
Flow
diagram:
The
flow diagram of the project is shown in Figure 2. At the beginning of the
program the I/O direction is specified. A byte variable called Cnt is used
as the loop variable. The program consists of an indefinite loop and at the
beginning of the loop the switch is tested. If the switch is logic 1 (i.e.
switch is not pressed) then the scrolling is to the left and if the switch is
pressed the switch is at logic 0 and scrolling is to the right. A 250 ms delay
is used between each output.
Software:
Pic Basic
The software for
PicBasic language is given in Figure 3. At the beginning of the program PORTA,
PORTB, TRISA, TRISB, and CMCON register addresses are defined. TRISA is set to
1 so that bit 0 of PORTA is configured as an input port. Similarly, TRISB is
cleared to 0 so that all bits of PORTB are configured as outputs. Push-button
switch is connected to bit 0 of PORTA (RA0). Normally this pin is pulled high
to logic 1 by using a resistor. When the switch is pressed the pin goes down to
logic 0. PORTA pins on the PIC16F627 microcontroller have dual functions and
they can either be used as analog comparator inputs, or as digital I/O ports. CMCON
register is used to control the function of these pins. Setting CMCON to 7
configures PORTA
pins as digital I/O ports. Inside the LOOP, the value of Cnt is sent to
PORTB and the PEEK instruction is used to read the switch setting. “Bit0”
refers to bit 0 of variable “B0” which is where the switch is connected. When
the switch is pressed the program jumps to label PRESSED where the LEDs are
scrolled right. When the switch is not pressed the LEDs are scrolled left. This
loop is repeated forever with 250 ms delay between each output. Set port
directions
Figure
2 Flow
diagram
‘*************************************************************************
‘ RIGHT-LEFT SCROLLING LEDS
‘
=========================
‘ 8 LEDs are connected to PORTB of a PIC
microcontroller. This program
‘
scrolls the LEDs to the right or left depending on a switch setting. The switch
‘
is connected to bit 0 of PORT A. If the switch is not pressed the switch
‘
output is at logic 1 and the LEDs scroll to the left. When the switch is
‘
pressed the LEDs scroll to the right. A 250ms delay is used between each
‘
output.
‘*************************************************************************
‘ SYMBOLS
‘
Symbol
TRISA = $85 ‘
TRISA address
Symbol
TRISB = $86 ‘ TRISB address
Symbol
PORTA = $05 ‘
PORTA address
Symbol
PORTB = $06 ‘
PORTB address
Symbol
CMCON = $1F
‘ CMCON address
Symbol
Cnt = B1 ‘
Cnt is a byte variable
Symbol
Switch = B0 ‘
Switch is a byte variable
‘
‘
START OF MAIN PROGRAM
‘
POKE
CMCON, 7 ‘ RA0-RA3 are digital I/O
POKE
TRISA, 1
‘ Set PORTA bit 0 as input
POKE
TRISB, 0 ‘
Set all PORTB pins as outputs
INIT:
CNT
= 1 ‘
Initialise Cnt to 1
Figure
3 (Continued)
PicBasic
Pro
The
software for PicBasic Pro language is given in Figure 4. The PicBasic Pro
program is easier to understand. At the beginning of the program TRISB is
cleared to 0 to make all PORTB pins as outputs. Also, TRISA is set to 1 so that
bit 0 of PORTA is configured as input. CMCON
register
is set to 7 to configure PORTA pins as digital I/O. The switch setting is then
checked using an IF statement. When the switch is pressed bit 0 of PORTA goes
to logic 0 and the program scrolls the LEDs to right. When the switch is not
pressed bit 0 of PORTA is at logic
1
and the program scrolls the LEDs to the left.
LOOP:
POKE
PORTB, Cnt ‘
Send Cnt to PORTB
PAUSE
250 ‘
Wait 250ms
PEEK
PORTA, Switch ‘ Read switch setting
IF
Bit0 = 0 THEN PRESSED ‘ If switch is pressed
IF
Cnt = 128 THEN INIT
Cnt
= Cnt * 2 ‘
Shift Cnt left
GOTO
LOOP
PRESSED:
‘
Switch is pressed
IF
Cnt = 1 THEN NXT
Cnt
= Cnt / 2
GOTO
LOOP
NXT:
Cnt
= 128
GOTO
LOOP
END
‘ End of program
Figure
3 PicBasic
program
‘**************************************************************************
‘ RIGHT-LEFT SHIFTING LEDS
‘
========================
‘ 8 LEDs are connected to PORTB of a PIC16F627
microcontroller.
‘
This program scrolls the LEDs right or left depending on the mode of a
‘
push-button switch. When the switch is not pressed LEDs are scrolled left.
‘
When the switch is pressed, LEDs are scrolled right. A 250ms delay
‘
is used between each output.
‘*************************************************************************
‘ DEFINITIONS
Cnt
VAR Byte
‘ Declare Cnt as a Byte variable
‘ START OF MAIN PROGRAM
CMCON
_ 7 ‘ Set PORTA as digital I/O
TRISA
_ 1
‘ Set RA0 as input
TRISB
_ 0
‘ Set PORTB pins as outputs
INIT:
Cnt
_ 1
‘ Initialise Cnt to 1
LOOP:
PORTB
_ Cnt
‘ Send Cnt to PORTB
PAUSE
250
‘ Wait 250ms
IF
PORTA.0 _ 0 THEN
IF
Cnt _ 1 THEN Cnt _ 128: GOTO LOOP
Cnt
= Cnt >> 1
‘ Shift right
GOTO
LOOP
ELSE
IF
Cnt _ 128 THEN INIT
Cnt
_ Cnt << 1 ‘ Shift
left
GOTO
LOOP
ENDIF
END
‘
End of program
Figure 4 PicBasic Pro
program
No comments:
Post a Comment