Dynamic port bit in PIC 16F877a using loop

Publish the schematic. Its importent! A pin may get high or low upon closing depending on how it is connected.



Figure shows two common ways to interface switches to a microcontroller input. Input P0 uses R1 as a pull up. If SW1 is open, P0 will be high, and read as a logical 1. When SW1 is closed, pin P0 is shorted to ground, or 0V, and P0 will read as a logical 0.

P1 has R2 as a pull down resistor. When SW2 is open, P1 is pulled low, and read as a logical 0. Closing SW2 causes current to flow through R2, raising the voltage at P1 to the Vcc level. At that point P1 will read as a logical 1.

Note that some microcontrollers have internal pull up resistors that can be enabled under program controller. You don’t need to wire up R1 if you use an internal pull up resistor. If you use an external pull up resistor, tie the high end to the same voltage used to run the microcontroller. Using a higher voltage will damage the microcontroller, and a lower voltage may result the circuit not working.

More details and Selecting Resistor Values---> see Interfacing switches to microcontrollers

This is my proteus file

screenshot of the circuit

Looking at your previous code, you should use:
TRISD = 0x0F;

I don't know how detailed is Proteus' simulation, but you should use pull down resistors on the inputs and limiting resistor on LEDs.

You must pull high the MCLR pin for PIC to work.

varunme said:

This is my proteus file

Click to expand...

It can't work. Too many mistakes.

it may better work on a real hardware than in simulation isnt it ?

varunme said:

it may better work on a real hardware than in simulation isnt it?

Click to expand...

Not unless you want to burn up your LEDs, as Bjuric commented you need current limiting resistors and pull up or pull down resistors on your switches. Also as commented early, TRISD = 1 only sets the first pin of the PORTD, RD0, as input for the entire PORTD to be correctly configured as inputs use TRISD = 0xFF. Although TRISD is set to 0xFF and PSPMODE is disabled on reset , so I doubt that is your problem. If I have time I will modify your simulation in Proteus and see if I can get your code to perform as expected.

BigDog

extremely sorry, BigDogGuru. My fault. It should be TRISD=0xFF. Corrected above now.

papunblg said:

extremely sorry, BigDogGuru. My fault. It should be TRISD=0xFF. Corrected above now.

Click to expand...

Not a fault actually, its a way of tightening our toolsuite.

The code didnt worked on an actual hardware too

varunme said:

The code didnt worked on an actual hardware too

Click to expand...

Sir Varunme,
Happy New Year.

The following code (published earlier) has been tested on actual hardware and giving desired result:-
Remember that the code is tested on an old board where port A and Port B were pulled up using 1K resistors , so the result is some different according to the connection. Here If I close a switch on PORTA, an LED goes off at PORTB.

I also tested some of the other codes published above, they are also giving correct results. It appears that the problem you are facing due to Hardware connection. Modify your Hardware as BigDogGuru suggested already Also read the datasheet for correct settings of multi function pins.

#include <htc.h> //Hitech C compiler and 16F876a micro
#define _XTAL_FREQ 20000000
__CONFIG(FOSC_HS & WDTE_OFF & LVP_OFF & CPD_OFF & WRT_OFF & DEBUG_OFF & CP_OFF);


main(void)
{
unsigned char mybyte;
ADCON1=6;
TRISA=0xFF;
TRISB=0;

while(1){
mybyte=PORTA;
__delay_ms(50);
PORTB=mybyte;
}
}

Remember use of PULL UP or PULL Down for switches change the logic .

I have modified the proteus file , its working with single switch but not with the looped switch

View attachment Loop.zip

I dont use proteous simulator so could not open files present in Loop.zip. A schematic would be more useful.

This is the schematic showing standard connection(But remember that I have tested above codes using 16F876a:-

modified schematic in proteus