1.4.2.1. Hardware/Software Interface

The assembly program reads the ADC assigning writing to the ADC control register (address $1030). The baud rate is set by writing to the baud rate register (address $102B).

There are 256 bytes of RAM at $0000-$00FF and 512 bytes of EEPROM at locations $B600-$B7FF. There is ROM at $E000-$FFFF. Locations $0036-$00FF are reserved. The following is the assembly program code list:

.OUTA   EQU     $FFB8   * output the contents of the A register
BAUDREG EQU     $102B   * address of the baud rate control register
SCSR    EQU     $102E   * address of the SCI status register
SCDAT   EQU     $102F   * address of the SCI data register
ADCTL   EQU     $1030   * address of the A/D control register
ADC2    EQU     $1031   * address of the A/D result register 2
DELAY   EQU     $E2D9   * address of subroutine DELAY
NOTEON  EQU     $90     * noteon message
VEL     EQU     $40     * velocity (duration) of the midi note
        ORG     $0000   * start of the program

BEGIN   LDAA    #$20    * set BAUD rate to 31.25K
        STAA    BAUDREG * output the BAUD rate
REPEAT  LDAA    #noteon * A = 90   (noteon message)
OUT1    LDAB    SCSR    * B = SCI status 
        BITB    #$80    * test bit7 of B
        BEQ     OUT1    * if bit7=1, i.e., SCI still busy, then wait
        STAA    SCDAT   * else output A (noteon message)
NEWVOL  LDAB    #$02    * select ADC2
        STAB    ADCTL   * by modifying ADCTL
        LDAA    ADC2    * then load an arbitrary number as NOTE NUMBER
        LDAB    #$08    * number of times calling DELAY = 9
WAIT    JSR     DELAY   * call DELAY subroutine
        DECB            * B = B1
        BNE     WAIT    * repeat calling DELAY for 9 times
        PULB            * pop B
        PSHB            * push B, used to get old note number
        CBA             * compare A and B
        BEQ     NEWVOL  * if (A==B), then read another number
        JSR     .OUTA   * if not equal, output the new note number
        PULB            * pop B
        TAB             * B = A
        PSHB            * push B, update the old note number
        LDAA    #VEL    * note velocity = $40
        JSR     .OUTA   * output note velocity
        BRA     REPEAT  * repeat reading another number (a relative jump)
        SWI             * software interrupt

The OUTA subroutine outputs the A accumulator to the serial port.

[ Index | Main Paragraph ]