#include <REG8253.H>
;------------------------------------------------
; Reservierung des Stack-Bereichs
?STACK SEGMENT IDATA		
	RSEG	?STACK         
	DS	10H	
;------------------------------------------------------------------------------
; Auf Adresse 0 im Code-Speicher muss ein LJMP zum Programmanfang stehen
	CSEG    AT  0           ;absolutes Code-Segment bei Adresse 0
	ljmp    start           ;Springe zur Marke start
;------------------------------------------------------------------------------
; Hier folgt Programmcode (Code-Beginn ueber Linker festgelegt)
program_code   SEGMENT CODE
        RSEG   program_code     ;waehle Code-Segment
        USING   0               ;Zeige Benuetzung von Registerbank 0 fuer den folgenden Programmcode an
;------------------------------------------------------------------------------
;Initialisierung  Stack und I/O-Karte
start:
	mov sp,#?stack-1	;STACK-Definition
;------------------------------------------------------------------------------

phase_a         equ     p3.2
phase_b         equ     p3.3
led_port        equ     p0

        dseg    at 30h
enc_delta:      ds 1
enc_last:       ds 1

        cseg

main:
        call    poll_encoder
        call    read_encoder2
        add     a, led_port
        mov     led_port, a
        jmp     main

poll_encoder:
        clr     a
        mov     c, phase_a              ; input phase_a
        rlc     a
        jnb     phase_b, _poen1         ; input phase_b
        xrl     a, #3                   ; convert gray to binary
_poen1:
        xch     a, enc_last             ; store new as next last
        subb    a, enc_last             ; difference last - new
        jnb     acc.0, _poen3           ; bit 0 = value (1)
        jnb     acc.1, _poen2           ; bit 1 = direction (+/-)
        inc     enc_delta
        ret
_poen2:
        dec     enc_delta
_poen3:
        ret

read_encoder2:                          ; read two phase encoder
        mov     a, enc_delta            ; read delta counts
        anl     enc_delta, #1           ; clear all bits except debouncing bit
        mov     c, acc.7                ; copy sign bit
        rrc     a                       ; / 2
        ret

end