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128 lines
4.0 KiB
Plaintext
128 lines
4.0 KiB
Plaintext
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; c02 Program Initialization Code for Unexpanded VIC-20
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;ASCII Control Codes Equivalents
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CR EQU $0D ;Carriage Return
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LF EQU $11 ;Line Feed (Cursor Down)
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DEL EQU $14 ;Delete
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HT EQU $1D ;Horizontal Tab (Cursor Right)
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VT EQU $91 ;Vertical Tab (Cursor Up)
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FF EQU $93 ;Form Feed (Clear Screen)
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BS EQU $9D ;Backspace (Cursor Left)
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;PETSCII Key Mappings
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DELKEY EQU $14 ;Delete/Backspace Key (Delete)
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ESCKEY EQU $03 ;Escape/Stop Key (RUN/STOP)
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RTNKEY EQU $0D ;Return/Enter Key (RETURN)
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;Standard Library Constants
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FOMAX EQU 7 ;Maximum Number of Open Files
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FNMAX EQU 16 ;Maximum Filename Length
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;Zero Page Locations
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SRCLO EQU $FB ;String Pointer (stdio.asm)
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SRCHI EQU $FC ;Free Byte for User Programs
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DSTLO EQU $FD ;Free Byte for User Programs
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DSTHI EQU $FE ;Free Byte for User Programs
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;Other RAM Locations
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TEMP0 EQU $0310 ;Free Byte for User Programs
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TEMP1 EQU $0311 ;Free Byte for User Programs
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TEMP2 EQU $0312 ;Free Byte for User Programs
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TEMP3 EQU $0313 ;Free Byte for User Programs
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FTBL EQU $0334 ;File Table (files.a02)
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TBFFR EQU $033C ;Cassette I/O Buffer
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user12 EQU $03FC ;Free Byte for User Programs
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user13 EQU $03FD ;Free Byte for User Programs
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user14 EQU $03FE ;Free Byte for User Programs
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STKPTR EQU $03FF ;Stack Pointer Storage
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;Video RAM and ROM
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VICSCN EQU $1E00 ;Video Screen Memory Area (Unexpanded)
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CHRROM EQU $8000 ;Character Generator ROM
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VICCLR EQU $9600 ;COLOR RAM (UNEXPANDED)
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;Kernal Routines
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SETMSG EQU $FF90 ;Control System Message Output
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SETLFS EQU $FFBA ;Set up Logical File
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READST EQU $FFB7 ;Read Status Word
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SETNAM EQU $FFBD ;Set File Name
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OPEN EQU $FFC0 ;Open a Logical File
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CLOSE EQU $FFC3 ;Close Logical File
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CHKIN EQU $FFC6 ;Open Channel for Input
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CHKOUT EQU $FFC9 ;Open Channel for Output
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CLRCHN EQU $FFCC ;Clear I/O Channels
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CHRIN EQU $FFCF ;Input Character to Channel
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CHROUT EQU $FFD2 ;Output Character to Channel
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GETIN EQU $FFE4 ;Read Character from Keyboard Buffer
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CLALL EQU $FFE7 ;Close All Files
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;Machine Language Basic Stub
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ORG $A000 ;Start
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START: TSX ;Get Stack Pointer
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STX STKPTR ;and Save for Exit
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JMP MAIN ;Execute Program
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EXIT: LDX STKPTR ;Retrieve Saved Stack Pointer
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TXS ;and Restore It
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RTS ;Return to BASIC
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;Poll Keyboard for Character
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PLKEY EQU GETIN ;Read Character from Keyboard Buffer
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;Get Character from Keyboard
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GETKEY:
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;Wait for Character from Keyboard
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RDKEY: JSR PLKEY ;Poll Keyboard
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BEQ GETKEY ;If No Key, Loop
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RTS
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;Print Character to Console
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PRCHR EQU CHROUT ;
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;Delete Previous Character
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DELCHR: LDA #$9D ;Load Cursor Left into Accumulator
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JSR PRCHR ; and Print it
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LDA #$14 ;Load Delete into Accumulater
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JMP PRCHR ; and Print it
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;Advance Character to Next line
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NEWLIN: LDA #$0D ;Load C/R into Accumulator
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JMP PRCHR ; and Print it
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;Print Byte as Two-Digit Hex Number to Console
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PRBYTE: PHA ;Save Accumulater
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LSR ;Shift Hi Nybble to Low Nybble
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LSR
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LSR
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LSR
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JSR PRHEX ; and Print it
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PLA ;Restore Accumulator
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; and fall into prhex
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;Print Low Nybble as Hex Digit to Console
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PRHEX: AND #$0F ;Strip High Nybble
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CMP #$0A ;If Low Nybble >= 10
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BCC PRHEXC ;
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ADC #$06 ; Convert ':' to 'A'...
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PRHEXC: ADC #$30 ;Convert to ASCII Character
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JMP PRCHR ;Print Hex Digit and Return
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;Functions to set String Pointers
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;Used by memory, stdio, stdlin, string, and stringx libraries
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;Initialize Destination String Pointer and Index
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SETDST: STX DSTLO ;Save Destination String Pointer
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STY DSTHI
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RTS
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;Initialize Source String Pointer and Index
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SETSRC: STX SRCLO ;Save Source String Pointer
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STY SRCHI
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LDY #$00 ;Initialize Index Into String
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RTS
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;Retrieve Source String Pointer
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GETSRC: LDX SRCLO
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LDY SRCHI
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RTS
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**
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