How to interface LEDs with PIC Microcontroller (PIC18F4550)




It is necessary to understand basic I/O operations of PIC18F4550 before dealing with its complexities. This article presents a way to take simple output from a PIC microcontroller. This learning would also help in interfacing of external devices with the controller. Here the output from the microcontroller is taken on a set of LEDs which are made to blink in an alternate fashion.

PIC18F4550 has a total of 35 I/O (input-output) pins which are distributed among 5 Ports. The following table shows the names and numbers of I/O pins of these 5 ports: 

Port Name
Number of Pins
Pins
PORTA
7
RA0-RA6
PORTB
8
RB0-RB7
PORTC
7
RC0-RC2, RC4-RC7
PORTD
8
RD0-RD7
PORTE
4
RE0-RE3
 
Fig. 2: I/O pins name and numbers of various ports in PIC 
 
As opposed to a basic 8051 microcontroller like AT89C51 which has most of the port pins serving single function, the port pins of a PIC microcontroller are multiplexed to serve more than one purpose.
 
The 35 I/O pins of PIC18F4550 are also multiplexed with one or more alternative functions of controller’s various peripherals. Each Port of a PIC microcontroller corresponds to three 8-bit registers which should be configured to use the Port for general I/O purpose. These registers are:
 
1.            TRISx: This is a data direction register which sets the direction of each port pin as input or output.
2.            PORTx: This register stores the input level of pins (High or Low). When a pin configured as input, the input signal from external source is read from PORTx register.
3.            LATx: This is output latch register. The data which has to be sent to external hardware as output is stored in LATx register.
 
Port Description:
 
PORTA:
PortA has 7 pins which can be used as both input as well as output pin. The 7th bit is missing from all the three registers. The input and output given to this port are of 8-bit but the 8th bit is internally masked.
 
 
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TRISA
TRISA6
TRISA5
TRISA4
TRISA3
TRISA2
TRISA1
TRISA0
PORTA
RA6
RA5
RA4
RA3
RA2
RA1
RA0
LATA
LATA6
LATA5
LATA4
LATA3
LATA2
LATA1
LATA0
 
Fig. 3: PortA Configuration in PIC
PORTB:
PortB has 8 pins which can all be used for both input and output operation.
 
 
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TRISB
TRISB7
TRISB6
TRISB5
TRISB4
TRISB3
TRISB2
TRISB1
TRISB0
PORTB
RB7
RB6
RB5
RB4
RB3
RB2
RB1
RB0
LATB
LATB7
LATB6
LATB5
LATB4
LATB3
LATB2
LATB1
LATB0
 
Fig. 4: PortB Configuration in PIC 
PORTC:
PortC has 7 I/O pins. In PortC, Bit 3 is missing in hardware and Pins 4 & 5 can only be used as input pins. There are no 4th & 5th latch bits in LATC register, so these bits are internally masked during 8-bit write operation on PortC.
 
 
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TRISC
TRISC7
TRISC6
TRISC2
TRISC1
TRISC0
PORTC
RC7
RC6
RC5
RC4
RC2
RC1
RC0
LATC
LATC7
LATC6
LATC2
LATC1
LATC0
 
Fig. 5: PortC Configuration in PIC 
 
PORTD:
PortD has 8 pins which can all be used for both input and output operation.
 
 
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TRISD
TRISD7
TRISD6
TRISD5
TRISD4
TRISD3
TRISD2
TRISD1
TRISD0
PORTD
RD7
RD6
RD5
RD4
RD3
RD2
RD1
RD0
LATD
LATD7
LATD6
LATD5
LATD4
LATD3
LATD2
LATD1
LATD0
 
Fig. 6: PortD Configuration in PIC 
PORTE:
PortE has 4 I/O pins. Pin3 can be used as input pin only. RDPU bit is used to enable/disable internal pull-ups of PortD.
 
 
Bit 7
Bit 6
Bit 5
Bit 4
Bit 3
Bit 2
Bit 1
Bit 0
TRISE
TRISE2
TRISE1
TRISE0
PORTE
RPDU
RE3
RE2
RE1
RE0
LATE
LATE2
LATE1
LATE0
 
 Fig. 7: PortE Configuration in PIC
 
I/O configuration: 
The TRISx register is configured to set a pin as input or output. The High value (1) sets a pin as input pin and Low value (0) sets a pin as output. An easy way to remember this is to consider the resemblance of 1 with the letter I (for input) and  with the letter (for output).        
 
For example suppose a switch is connected at RB0 and an LED is connected to RB7 of PortB. Now the pins 0 & 7 have to be configured as input and output respectively. So the bit TRISB0 is set to 1 to configure RB0 as input pin & bit TRISB7 is set to 0 to configure RB7 as output pin. 
 
TRISB
TRISB7
TRISB6
TRISB5
TRISB4
TRISB3
TRISB2
TRISB1
TRISB0
Value
1
 
Fig. 8: TRISB0 set as 1 to configure RB0 as input to interface LED in PIC 
 
The unused bits are set to 0.
 
TRISB
TRISB7
TRISB6
TRISB5
TRISB4
TRISB3
TRISB2
TRISB1
TRISB0
Value
1
 
So the overall value of TRISB register becomes:
Using this knowledge, the objective of this article can be achieved which is to glow a set of LEDs in alternate blinking fashion. The LEDs here are connected to PORTB pins as shown in the circuit diagram.
 
Programming steps: 
 
1.      Configure the TRISB register to make PortB as output port.
2.      Set all the bits of LATB register High (1) to glow all LEDs.
3.      Provide some delay.
4.      Set all the bits of LATB register Low (0) to turn off the LEDs.
5.      Provide some delay.
6.      Repeat the process from step 2.

Project Source Code

###

READ  How to work with External (Hardware) Interrupts of PIC Microcontroller (PIC18F4550)




/******************Chip config*******************

PLLDIV = 5
CPUDIV = OSC1 / 2
USBDIV = 2
FOSC = HIGH_SPEED HS
FCMEN = OFF
IESO = OFF
PWRT = OFF
BOR = OFF
BORV = 3
VREGEN = OFF
WDT = OFF
WDTPS = 1:32768
CCP2MX = ON
PBADEN = OFF
LPT1OSC = OFF
MCLRE = OFF
STVREN = ON
LVP = OFF
ICPRT = OFF
XINST = OFF
DEBUG = OFF
CP0 = OFF, CP1 = OFF, CP2 = OFF, CP3 = OFF
CPB = OFF
CPD = OFF
WRT0 = OFF, WRT1 = OFF, WRT2 = OFF, WRT3 = OFF
WRTC = OFF
WRTB = OFF
WRTD = OFF
EBTR0 = OFF, EBTR1 = OFF, EBTR2 = OFF, EBTR3 = OFF
EBTRB = OFF

******************Chip config*******************/

#include <p18cxxx.h>

void delay_ms ( int delay );

void delay_ms ( int delay )
{
int ms, i;

for ( ms = 0; ms < delay; ms ++ )
for ( i = 0; i < 5; i ++ );
}

void main()
{
TRISB = 0x00; // Set PORTB as output PORT
LATB = 0xFF; // Set PORTB high initially (All LEDs on)

while ( 1 )
{
LATB = ~LATB; // Toggle the value of PORTB
delay_ms ( 1000 ); // Delay of 1 sec
}
}
###

Circuit Diagrams

Circuit Diagrams ......

Project Components

Project Video




Source: How to interface LEDs with PIC Microcontroller (PIC18F4550)




Current Project / Post can also be found using:

  • microcontroller for led lights
  • Interface an LED to PORTC pin 0 via a breadboard and a switch to PORTB pin 0

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