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#include <avr/io.h>
#include <avr/interrupt.h>
#undef _SFR_IO8
#define _SFR_IO8(x) (x)
#undef _SFR_IO16
#define _SFR_IO16(x) (x)
#define USED_OUT_PIN 0x04 // B2
#define USED_IN_PIN 0x08 // B3
; the pins should be be connected as follows:
; USED_OUTPUT_PIN should drive a open drain transistor circuit
; The open drain output is connected to an external pull up
; the USED_IN_PIN should rout the open drain result, which is simply inverse to the USED_OUT_PIN
.global main
main:
ldi r16, USED_OUT_PIN ; only one output pin
out DDRB, r16 ; all pins output
ldi r16, 0x00
out PORTB, r16
nop ; in real device e need one instruction before reading the result back
in r17, PINB ; should have USED_IN_PN high and USED_OUT_PIN low -> 0x08 -> r17
ldi r16, USED_OUT_PIN
out PORTB, r16
nop
in r18, PINB ; should have USED_IN_PIN low and USED_OUT_PIN high -> 0x04 -> r18
stopsim:
nop
endless:
rjmp endless
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