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        ;; *******************************************************************

        ;; $Id: test.asm 179 2009-04-01 19:48:38Z arniml $

        ;;

        ;; Test the MICROBUS functionality.

        ;;

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

        org     0x00

        clra

        ;; init counter with 0

        xad     3, 15

        ;;

        ;; microbus data is written to RAM register 0&1, digits 0-11

        ;;

read_next_char:

        ;; request data

        ogi     0x1

poll_write:

        skgbz   0

        jp      poll_write

        ;; read posted data

        cqma

        x       1               ; put A to R0, Q[3:0]

        x       1               ; put M to R1, Q[7:4]

        ;; check increment

        ldd     3, 15

        aisc    0x1

        cab                     ; set new Bd

        xad     3, 15

        aisc    0x5             ; check for old Bd == 0xb

        jmp     read_next_char

        ;;

        ;; output received string

        ;;

        ;; init counter with 0

        clra

        cab

        xad     3, 15

write_next_char:

        ld      1

        ld      1               ; load A from    R1, Q[7:4]

                                ; present M from R0, Q[3:0]

        camq

        ;; request read

        ogi     0x1

poll_read:

        skgbz   0

        jp      poll_read

        ;; check increment

        ldd     3, 15

        aisc    0x1

        cab                     ; set new Bd

        xad     3, 15

        aisc    0x5             ; check for old Bd == 0xb

        jmp     write_next_char

        jmp     .