Lecture 44 : Blinking LED with PIC16F877A

Objective To demonstrate blinking of an LED interfaced with PIC16F877A Description: A LED is connected to RA0 pin of Port A. This pin has built-in internal pull-up which can source a current of up to 25mA. The circuit diagram is shown as follows - Fig 44.1  Circuit diagram for blinking LED experiment Assembly Code: Sampling an analog signal periodically and displaying its digital value using PIC16F877A Aim To continuously sample convert an analog signal to its digital equivalent and read the digital value from one port of the PIC16C74A microcontroller Components/Software PIC16F877A microcontroller Programmer (to program the microcontroller) Computer System with Windows 98 or later operating system and RS-232 Cable +5v D.C Power Supply Resistors, Capacitors 10 MHz crystal oscillator Signal Generator and CRO Description An analog signal is converted to digital value using an A/D converter (which is in-built in the PIC microcontroller). After conversion is complete, the eight digital bits are written to Port D. The process is then repeated. The A/D conversion is done on an interrupt basis. Procedure Write the code using a desktop PC. Compile it and transfer it to the microcontroller using the programmer. Wire the microcontroller as shown in the diagram. Switch on the supply and push Reset button Observe the results Switch off the supply Assembly Code include PIC16F877A org 000H goto Mainline org 004H bcf PIR1, ADIF movf PORTD, w goto Mainline org 20H Mainline: bsf STATUS, RPO clrf ADCON1 movlw 30H movwf TRISA movlw 30H movwf TRISE bsf PIE1, ADIE bsf STATUS, RPO movlw 081H movwf ADCON0 bcf PIR1, ADIF bsf INTCON, PEIE bsf INTCON, GIE bsf ADCON, GO Observation The digital equivalents of the applied analog signal were observed. The digital bits were observed, one at a time, using the CRO. Conclusion: An analog signal is converted to digital one. The digital signal is observed at Port D of the PIC microcontroller. Circuit Diagram: