*
*``````````````````````````````*
* HEAD.REQUIRED                *
*                              *
* THIS HEADER MUST BE THE      *
* INCLUDED BEFORE ANY OTHER    *
* CODE IN ORDER FOR THE PROPER *
* FUNCTIONING OF ANY LIBRARY.  *
*                              *
* AUTHOR:    NATHAN RIGGS      *
* CONTACT:   NATHAN.RIGGS@     *
*            OUTLOOK.COM       *
*                              *
* DATE:      29-NOV-2019       *
* ASSEMBLER: MERLIN 8 PRO      *
* OS:        DOS 3.3           *
*                              *
* BYTES: 311                   *
*,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,*
*
* VARIABLE DECLARATIONS ********
*
** JUMP TABLE SETUP. THIS IS FOR LOADING
** SUBROUTINES INTO MEMORY FOR ACCESS BY
** EXTERNAL EXECUTIONS. NOTE THAT THIS
** SHOULD ALWAYS START AT SECOND BYTE OF
** CODE IN THE PROGRAM SO THAT ITS
** LOCATION IN MEMORY IS EASILY KNOWN.
*
JUMPTBL  JMP   MAIN_START ; ** ALWAYS ** START WITH
                          ; JUMP TO MAIN_START
         DS    32         ; 16 MORE ENTRIES
*
** 20 BYTES FOR VARIABLES
*
VARTAB   DS    20
*
** 256 BYTES DEDICATED TO RETURN
** VALUES OF VARIABLE LENGTH; CAN BE
** MODIFIED TO SUIT SMALLER OR LARGER
** NEEDS.
*
RETLEN   DS    1          ; RETURN VALUE BYTE LENGTH
RETURN   DS    255
*
** ADDRESS STORAGE LOCATIONS FOR
** INDIRECT ADDRESSING.
*
ADDR1    EQU   $06        ; AND $07
ADDR2    EQU   $08        ; AND $09
ADDR3    EQU   $EB        ; AND $EC
ADDR4    EQU   $ED        ; AND $EE
*
** SCRATCHPAD ZERO PAGE LOCATIONS AND
** DEDICATED ZERO PAGE ADDRESS TO HOLD
** A RETURN ADDRESS PASSED VIA THE STACK
*
SCRATCH  EQU   $19        ; USED TO BACKUP .Y
SCRATCH2 EQU   $1E
RETADR   EQU   $FE        ; AND $FF
*
** ZERO PAGE ADDRESSES DEDICATED TO PASSING
** BACK RESULTS WHEN THERE ARE MORE THAN
** THREE BYTES BEING PASSED (AXY) AND THE
** USE OF THE STACK IS IMPRACTICAL OR TOO SLOW
*
RESULT   EQU   $FA
RESULT2  EQU   $FC
*
** WORD AND BYTE PARAMETER SPACE USED
** BY APPLEIIASM MACROS
*
WPAR1    EQU   $FA
WPAR2    EQU   $FC
WPAR3    EQU   $FE
BPAR1    EQU   $EF
BPAR2    EQU   $E3
BPAR3    EQU   $1E
BPAR4    EQU   $19
*
** VARIOUS HOOKS USED BY ALL ROUTINES
*
REENTRY  EQU   $3D0
*
PROMPT   EQU   $33        ; DOS PROMPT CHARACTER
COLDENT  EQU   $03D3      ; COLD ENTRY TO DOS
SRESET   EQU   $03F2      ; SOFT RESET
PRNTAX   EQU   $F941      ; PRINT HEX VALS OF A,X REGISTERS
BELL     EQU   $FBE4      ; RING MY BELL
IOSAVE   EQU   $FF4A      ; SAVE CURRENT STATE OF REGISTERS
IOREST   EQU   $FF3F      ; RESTORE OLD STATE OF REGISTERS
*
BITON0   EQU   $01        ; FOR AND MASKING
BITON1   EQU   $02        ; TO CHECK IF BIT IS ON
BITON2   EQU   $04
BITON3   EQU   $08
BITON4   EQU   $10
BITON5   EQU   $20
BITON6   EQU   $40
BITON7   EQU   $80
*
MAIN_START