C language or assembly

Question

1.4 Write a function/subroutine that reads the switch on PB3. (Either C or Assembly is acceptable) (If writing in assembly, return the result in R6)

char S2Read() // Read S2 (bottom most). Return 0xFF if pressed, and 0x00 if not pressed.

Answer 1

a simple way to implement that in C, assuming PB3 corresponds to Port B, bit 3 and that reading a 1 means the switch is not pressed and 0 means pressed:

#include <stdint.h>

#include <avr/io.h> // adjust depending on your MCU

char S2Read() {

// Check PB3 input pin

if (PINB & (1 << 3)) { // PB3 is high

return 0x00; // Not pressed

} else {

return 0xFF; // Pressed

}

}

If you want an Assembly version (for 8-bit AVR, returning the result in R6):

; Assume PORTB input, PB3

; Returns 0xFF in R6 if pressed, 0x00 if not

S2Read:

in r6, PINB ; Read Port B

sbrs r6, 3 ; Skip next if PB3 is set (not pressed)

ldi r6, 0xFF ; PB3 = 0 (pressed)

ret

ldi r6, 0x00 ; PB3 = 1 (not pressed)

ret