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        ;; *******************************************************************
        ;; $Id: test.asm,v 1.2 2006-05-27 22:46:29 arniml Exp $
        ;;
        ;; Checks the XAS instruction.
        ;;

        ;; the cpu type is defined on asl's command line

        org     0x00
        clra

        ;; *******************************************************************
        ;; Test counter functionality
        ;;
        lei     0x5
        ;; enable counter
        clra
        camq

        ;; clear SKL
        xas
        nop                     ; spend some time to let effect of SKL
        nop                     ; falling edge pass by
        nop                     ;

        ;; -------------------------------------------------------------------
        ;; step 1
        ;; decrement counter from 1 to 0
        ;; test SO by controlling SI via SO
        ;; 
        ;; load 0x1 to counter
        clra
        aisc    0x1
        xas
        ;; decrement via SO
        lei     0xd
        nop                     ; ensure minimum '1' duration
        lei     0x5
        nop                     ;
        nop                     ; ensure minimum '0' duration
        nop                     ;
        xas
        ;; check for 0x0
        xad     3, 15
        clra
        x       0
        xad     3, 15
        ske
        jmp     fail

        ;; -------------------------------------------------------------------
        ;; step 2
        ;; decrement counter from 0 to 0xf
        ;; test SKL by controlling SI via SK
        ;;
        ;; set SKL to '1'
        sc                      ; SKL = '1'
        xas
        ;; load 0x0 to counter, decrement via SK
        clra
        rc
        xas
        nop                     ;
        nop                     ; ensure minimum '0' duration
        nop                     ;
        xas
        ;; check for 0xf
        xad     3, 15
        clra
        aisc    0xf
        x       0
        xad     3, 15
        ske
        jmp     fail


        ;; -------------------------------------------------------------------
        ;; step 3
        ;; check minimum high time on SI
        ;;
        ;; load 0x0 to counter
        clra
        xas
        ;; clock on SI
        lei     0xd
        lei     0x5             ; high time too short
        nop                     ;
        nop                     ; ensure minimum '0' duration
        nop                     ;
        xas
        ;; check for 0x0
        xad     3, 15
        clra
        x       0
        xad     3, 15
        ske
        jmp     fail

        ;; -------------------------------------------------------------------
        ;; step 4
        ;; check minimum low time on SI
        ;;
        ;; load 0x0 to counter
        clra
        xas
        ;; clock on SI
        lei     0xd
        nop                     ; ensure minimum '1' duration
        lei     0x5
        lei     0xd             ; low time too short
        xas
        ;; check for 0x0
        xad     3, 15
        clra
        x       0
        xad     3, 15
        ske
        jmp     fail


        ;; *******************************************************************
        ;; Test shift register functionality
        ;;
        lei     0xc             ; SO = SIO output
        ;; enable shift register
        aisc    0x1
        camq

        ;; shift out 0x5
        aisc    0x4
        sc
        xas
        ;;
        nop                     ;
        nop                     ; shift for four clocks on SK
        rc                      ;
        xas                     ; stop SK
        ;; check for 0x2
        xad     3, 15
        clra
        aisc    0x2
        x       0
        xad     3, 15
        ske
        jmp     fail

        ;; shift out 0x0
        clra
        sc
        xas
        ;;
        nop                     ;
        nop                     ; shift for four clocks on SK
        rc                      ;
        xas                     ; stop SK
        ;; check for 0x8
        xad     3, 15
        clra
        aisc    0x8
        x       0
        xad     3, 15
        ske
        jmp     fail

        ;; now disable SO and check that only '0' is shifted in
        lei     0x4             ; SO = '0'
        ;; shift out 0xf
        clra
        aisc    0xf
        sc
        xas
        ;;
        nop                     ;
        nop                     ; shift for four clocks on SK
        rc                      ;
        xas                     ; stop SK
        ;; check for 0x0
        xad     3, 15
        clra
        x       0
        xad     3, 15
        ske
        jmp     fail

        ;; enable SO
        lei     0xc
        ;; shift out 0x1 to force SI to '1' via SO
        clra
        aisc    0x1
        sc
        xas
        ;;
        nop                     ;
        nop                     ; shift for four clocks on SK
        rc                      ;
        xas                     ; stop SK
        ;; shift out 0x0 with disabled SK
        clra
        xas
        ;;
        nop                     ;
        nop                     ; shift for four clocks on SK
        nop                     ;
        xas
        ;; check for 0xf
        xad     3, 15
        clra
        aisc    0xf
        x       0
        xad     3, 15
        ske
        jmp     fail

        jmp     pass

        org     0x100
        include "pass_fail.asm"