pic 16f877 with keypad

[PA3040]

Dear all

please advice me how may I scan and recognize witch number press from
the key board ( 0 to 9 ) connected to portb

my most prefer language is assembly

 

[wp100]

Hi,

See this good tutorial for all hardware and software details

PIC Tutorial* Nine - HEX Keypad

 

[PA3040]

Dear all can we use A/D converter to recognised the key in key pad
that mean, each keys has unique resistance
can somebody explain it more

thanks in advance

 

[wp100]

Hi,

See this Microchip pdf, tip #7.
https://ww1.microchip.com/downloads/en/devicedoc/40040b.pdf

Basically the resistors to each key form a potential divider from the 5V supply to the adc i/o pin.
You carefully select the values to create an suitably spaced voltage for the 16 keys across the 5v range, so when you read the keys voltage into a ADC port you can work out which key was pressed.

When selecting your resistors ensure you have a total of at least 2k for any key otherwise you will risk shorting out the +5v rail.
Electronics 2000 | Potential Divider Calculator

 

[PA3040]

Dear wp100
Thanks for reply

as per this method, if resister or supply voltage will changed how MCU recognise actual key

 

[wp100]

Hi,

It would take too long to explain it all here.

You first need to do some basic tests with a simple adc routine using a 10k pot as the input source, so you understand how it works, then the answer for you keypad should become clear.

Have a look at that Winpicprog ADC tutorial which gives a good description of the software.
However his extra ADC input hardware is not needed for a simple voltage test, just feed the 10k pots slider directly to the adc pin.

Also see this sites ADC lesson
**broken link removed**

 

[PA3040]

Dear All
what is the most precise method to recognize a key in the key pad in between AD converter and
PORTB change( interrupted ) methods
Thanks in advance

 

[PA3040]

Dear all
if we configure portb as input
then we

movlw 0xff
movwf portb

and then read the port

movf portb,w
movwf result ; result register

so in MPLAB SIM result is
result = 0x00
but anther simulator (PIC SIMULATOR IDE) result is 0xff

PLEASE ADVICE

 

[wp100]

Hi,

To set the Port to Input or Output you use the TRIS instruction.

banksel TRISB
movlw 0xFF
movwf TRISB
banksel PORTB

movf PORTB,W