C02/vic20/include/vic20.a02

; c02 Program Initialization Code for Unexpanded VIC-20

;ASCII Control Codes Equivalents
CR      EQU $0D   ;Carriage Return
LF      EQU $11   ;Line Feed (Cursor Down)
DEL     EQU $14   ;Delete
HT      EQU $1D   ;Horizontal Tab (Cursor Right)
VT      EQU $91   ;Vertical Tab (Cursor Up)
FF      EQU $93   ;Form Feed (Clear Screen)
BS      EQU $9D   ;Backspace (Cursor Left)

;PETSCII Key Mappings
DELKEY  EQU $14   ;Delete/Backspace Key (Delete)
ESCKEY  EQU $03   ;Escape/Stop Key      (RUN/STOP)
RTNKEY  EQU $0D   ;Return/Enter Key     (RETURN)

;Standard Library Constants
FOMAX   EQU 7     ;Maximum Number of Open Files
FNMAX   EQU 16    ;Maximum Filename Length

;Zero Page Variables
PTRLO   EQU $35   ;System Pointer (pointer.a02)
PTRHI   EQU $36   ;NOTE: Overwritten by BASIC String Routines

BLKLO   EQU $50   ;Block Pointer (block.a02)
BLKHI   EQU $51   ;NOTE: Overwritten by BASIC String Routines

TIMEH   EQU $A0   ;Jiffy Clock High Byte
TIMEM   EQU $A1   ;Jiffy Clock Middle Byte
TIMEL   EQU $A2   ;Jiffy Clock Low Byte

SRCLO   EQU $FB   ;Source Pointer Low Byte (stdlib.a02, etc.)
SRCHI   EQU $FC   ;Source Pointer High Byte
DSTLO   EQU $FD   ;Destination Pointer Low Byte (stdlib.a02, etc.)
DSTHI   EQU $FE   ;Destination Pointer High Byte

;Page 1 RAM Locations (Unused Area at Bottom of Stack)
FTBL    EQU $0140 ;File Table (files.a02) Same on PET

;Other RAM Locations
TEMP0   EQU $0310 ;Temporary Variables
TEMP1   EQU $0311 ;Used by Library Functions
TEMP2   EQU $0312
TEMP3   EQU $0334 ;($0313 is Free on VIC-20 but not C64)
BLKLEN  EQU $0335 ;Block Segment Length
BLKSLO  EQU $0336 ;Block Start Address
BLKSHI  EQU $0337 
BLKELO  EQU $0338 ;Block End Address
BLKEHI  EQU $0339
;       EQU $033A ;Free Byte for User Programs
;       EQU $033B ;Free Byte for User Programs
TBFFR   EQU $033C ;Cassette I/O Buffer
;       EQU $03FC ;Free Byte for User Programs
RANDOM  EQU $03FD ;Seed for rand() Function
RDSEED  EQU $03FE ;Seed for random() Function
STKPTR  EQU $03FF ;Stack Pointer Storage

;Video RAM and ROM 
VICSCN  EQU $1E00 ;Video Screen Memory Area (Unexpanded)
CHRROM  EQU $8000 ;Character Generator ROM
VICCLR  EQU $9600 ;COLOR RAM (UNEXPANDED)

;Kernal Routines
SETMSG  EQU $FF90 ;Control System Message Output
SETLFS  EQU $FFBA ;Set up Logical File
READST  EQU $FFB7 ;Read Status Word
SETNAM  EQU $FFBD ;Set File Name
OPEN    EQU $FFC0 ;Open a Logical File
CLOSE   EQU $FFC3 ;Close Logical File
CHKIN   EQU $FFC6 ;Open Channel for Input
CHKOUT  EQU $FFC9 ;Open Channel for Output
CLRCHN  EQU $FFCC ;Clear I/O Channels
CHRIN   EQU $FFCF ;Input Character to Channel
CHROUT  EQU $FFD2 ;Output Character to Channel
GETIN   EQU $FFE4 ;Read Character from Keyboard Buffer
CLALL   EQU $FFE7 ;Close All Files

;Machine Language Basic Stub
        ORG $1001              ;Start 
BASIC:  DC  $0C, $10           ; Pointer to Next Line (4108)
        DC  $00, $00           ; Line Number (0)
        DC  $9E                ; SYS 
        DC  $20                ; ' '
        DC  $34, $31, $31 ,$30 ; "4110" 
        DC  $00                ;End of Line Marker
        DC  $00, $00           ;End of Basic Program

START:  TSX         ;Get Stack Pointer
        STX STKPTR  ;and Save for Exit
        LDA TIMEL   ;Load Jiffy Clock Low Byte
        STA RDSEED  ;and Store in Random Seed
        JMP MAIN    ;Execute Program

EXIT:   LDX STKPTR  ;Retrieve Saved Stack Pointer
        TXS         ;and Restore It
        RTS         ;Return to BASIC

;Poll Keyboard for Character
PLKEY   EQU GETIN   ;Read Character from Keyboard Buffer

;Get Character from Keyboard
GETKEY: 
;Wait for Character from Keyboard
RDKEY:  JSR PLKEY   ;Poll Keyboard
        BEQ GETKEY  ;If No Key, Loop
        RTS

;Print Character to Console
PRCHR   EQU CHROUT   ;

;Delete Previous Character
DELCHR: LDA #$9D     ;Load Cursor Left into Accumulator
        JSR PRCHR    ;  and Print it
        LDA #$14     ;Load Delete into Accumulater
        JMP PRCHR    ;  and Print it

;Advance Character to Next line
NEWLIN: LDA #$0D     ;Load C/R into Accumulator
        JMP PRCHR    ;  and Print it

;Print Byte as Two-Digit Hex Number to Console
PRBYTE: PHA         ;Save Accumulater
        LSR         ;Shift Hi Nybble to Low Nybble
        LSR 
        LSR 
        LSR 
        JSR PRHEX   ;  and Print it
        PLA         ;Restore Accumulator 
                    ;  and fall into prhex
                    
;Print Low Nybble as Hex Digit to Console
PRHEX:  AND #$0F    ;Strip High Nybble
        CMP #$0A    ;If Low Nybble >= 10
        BCC PRHEXC  ;  
        ADC #$06    ;  Convert ':' to 'A'...
PRHEXC: ADC #$30    ;Convert to ASCII Character
        JMP PRCHR   ;Print Hex Digit and Return

;Functions to set String Pointers
;Used by memory, stdio, stdlin, string, and stringx libraries

;Initialize Destination String Pointer and Index
SETDST: STX DSTLO       ;Save Destination String Pointer
        STY DSTHI
        RTS

;Initialize Source String Pointer and Index
SETSRC: STX SRCLO       ;Save Source String Pointer
        STY SRCHI
        LDY #$00        ;Initialize Index Into String
        RTS

;Retrieve Source String Pointer
GETSRC: LDX SRCLO
        LDY SRCHI
        RTS
**