RESET           CLD                     Clear decimal arithmetic mode
                CLI
                LDY     #%0111.1111     Mask for DSP data direction reg
                STY     DSP              (DDR mode is assumed after reset)
                LDA     #%1010.0111     KBD and DSP control register mask
                STA     KBDCR           Enable interrupts, set CA1, CB1 for
                STA     DSPCR            positive edge sense/output mode.
NOTCR           CMP     #BS             Backspace key?
                BEQ     BACKSPACE       Yes
                CMP     #ESC            ESC?
                BEQ     ESCAPE          Yes
                INY                     Advance text index
                BPL     NEXTCHAR        Auto ESC if line longer than 127
ESCAPE          LDA     #PROMPT         Print prompt character
                JSR     ECHO            Output it.
GETLINE         LDA     #CR             Send CR
                JSR     ECHO
                LDY     #0+1            Start a new input line
BACKSPACE       DEY                     Backup text index
                BMI     GETLINE         Oops, line's empty, reinitialize
NEXTCHAR        LDA     KBDCR           Wait for key press
                BPL     NEXTCHAR        No key yet!
                LDA     KBD             Load character. B7 should be '1'
                STA     IN,Y            Add to text buffer
                JSR     ECHO            Display character
                CMP     #CR
                BNE     NOTCR           It's not CR!
                LDY     #-1             Reset text index
                LDA     #0              Default mode is XAM
                TAX                     X=0
SETSTOR         ASL                     Leaves $7B if setting STOR mode
SETMODE         STA     MODE            Set mode flags
BLSKIP          INY                     Advance text index
NEXTITEM        LDA     IN,Y            Get character
                CMP     #CR
                BEQ     GETLINE         We're done if it's CR!
                CMP     #"."
                BCC     BLSKIP          Ignore everything below "."!
                BEQ     SETMODE         Set BLOCK XAM mode ("." = $AE)
                CMP     #":"
                BEQ     SETSTOR         Set STOR mode! $BA will become $7B
                CMP     #"R"
                BEQ     RUN             Run the program! Forget the rest
                STX     L               Clear input value (X=0)
                STX     H
                STY     YSAV            Save Y for comparison
NEXTHEX         LDA     IN,Y            Get character for hex test
                EOR     #$B0            Map digits to 0-9
                CMP     #9+1            Is it a decimal digit?
                BCC     DIG             Yes!
                ADC     #$88            Map letter "A"-"F" to $FA-FF
                CMP     #$FA            Hex letter?
                BCC     NOTHEX          No! Character not hex
DIG             ASL
                ASL                     Hex digit to MSD of A
                ASL
                ASL
                LDX     #4              Shift count
HEXSHIFT        ASL                     Hex digit left, MSB to carry
                ROL     L               Rotate into LSD
                ROL     H               Rotate into MSD's
                DEX                     Done 4 shifts?
                BNE     HEXSHIFT        No, loop
                INY                     Advance text index
                BNE     NEXTHEX         Always taken
NOTHEX          CPY     YSAV            Was at least 1 hex digit given?
                BEQ     ESCAPE          No! Ignore all, start from scratch
                BIT     MODE            Test MODE byte
                BVC     NOTSTOR         B6=0 is STOR, 1 is XAM or BLOCK XAM
                LDA     L               LSD's of hex data
                STA     (STL,X)         Store current 'store index'(X=0)
                INC     STL             Increment store index.
                BNE     NEXTITEM        No carry!
                INC     STH             Add carry to 'store index' high
TONEXTITEM      JMP     NEXTITEM        Get next command item.
RUN             JMP     (XAML)          Run user's program
NOTSTOR         BMI     XAMNEXT         B7 = 0 for XAM, 1 for BLOCK XAM
                LDX     #2              Copy 2 bytes
SETADR          LDA     L-1,X           Copy hex data to
                STA     STL-1,X          'store index'
                STA     XAML-1,X         and to 'XAM index'
                DEX                     Next of 2 bytes
                BNE     SETADR          Loop unless X = 0
NXTPRNT         BNE     PRDATA          NE means no address to print
                LDA     #CR             Print CR first
                JSR     ECHO
                LDA     XAMH            Output high-order byte of address
                JSR     PRBYTE
                LDA     XAML            Output low-order byte of address
                JSR     PRBYTE
                LDA     #":"            Print colon
                JSR     ECHO
PRDATA          LDA     #" "            Print space
                JSR     ECHO
                LDA     (XAML,X)        Get data from address (X=0)
                JSR     PRBYTE          Output it in hex format
XAMNEXT         STX     MODE            0 -> MODE (XAM mode).
                LDA     XAML            See if there's more to print
                CMP     L
                LDA     XAMH
                SBC     H
                BCS     TONEXTITEM      Not less! No more data to output
                INC     XAML            Increment 'examine index'
                BNE     MOD8CHK         No carry!
                INC     XAMH
MOD8CHK         LDA     XAML            If address MOD 8 = 0 start new line
                AND     #%0000.0111
                BPL     NXTPRNT         Always taken.
PRBYTE          PHA                     Save A for LSD
                LSR
                LSR
                LSR                     MSD to LSD position
                LSR
                JSR     PRHEX           Output hex digit
                PLA                     Restore A
PRHEX           AND     #%0000.1111     Mask LSD for hex print
                ORA     #"0"            Add "0"
                CMP     #"9"+1          Is it a decimal digit?
                BCC     ECHO            Yes! output it
                ADC     #6              Add offset for letter A-F
ECHO            BIT     DSP             DA bit (B7) cleared yet?
                BMI     ECHO            No! Wait for display ready
                STA     DSP             Output character. Sets DA
                RTS
                .DA     $0000           Unused, what a pity
NMI_VEC         .DA     $0F00           NMI vector
RESET_VEC       .DA     RESET           RESET vector
IRQ_VEC         .DA     $0000           IRQ vector