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                                 CHAPTER 5

                             ________________
                             OPERATING SYSTEM



     The system ROM in an ORGANISER MKII occupies the  memory  map  between
$8000 and $ffff.  The ROM is divided into a number of functional areas:

     1.  The operating system.

     2.  The OPL language.

     3.  The applications.


     This document is  mainly  concerned  with  describing  the  facilities
provided  by the operating system to application programmers.  Both the OPL
language and the applications (e.g.  the diary ) call the operating  system
via the standard operating system interface.



     ________________
5.1  SYSTEM INTERFACE

       _______________________
5.1.1  CALLING SYSTEM SERVICES

     The interface  to  the  operating  system  is  via  the  SWI  hardware
instruction  followed  by the vector number of the operating system service
required, i.e.

            SWI                 ; software interrupt
    .BYTE   VECTOR_NUMBER       ; required service vector
HERE:


     After execution of the SWI call, execution continues  after  the  byte
containing the vector number, at the label HERE in the example above.

     Parameters to the service are passed in one or more of the A,B (or D),
and  X  registers  and  for  a small number of services in memory locations
UTW_S0 and UTW_S1 which are zero page  locations.   Certain  services  also
require  information in the runtime buffer RTT_BF.  The description of each
service details the information required to be passed to it.   In  addition
the  results  of a system service are returned in the machine registers A,B
(or D) or X as required.  The addresses of UTW_S0 and UTW_S1 are  described
in chapter 6.



       _____________________
5.1.2  REGISTER PRESERVATION

     In general it should be assumed that all registers  (A,B  and  X)  are
trashed  by  system  services.   If  this  is  not the case then the system
service description will explicitly state which registers are preserved.



       ______________
5.1.3  ERROR HANDLING

     All system services which indicate that they have  error  returns  may
set  the  carry  flag  on exit from the system service and return the error
code in the B register.  Note that system services such as  KB$GETK,  which
do not return any errors, may not clear the carry flag.



       ____________
5.1.4  THE OS MACRO

     Throughout the operating system description examples will be  provided
which use a macro called OS which is as follows:

    .MACRO      OS      XX
    .BYTE       $3f,XX
    .ENDM


     Using this macro to get a key, for example, will be coded as follows:

    OS          KB$GETK


     and calling a system service which can return an error such as AL$GRAB
should be called as follows:

    CLR         A
    CLR         B
    OS          AL$GRAB
    BCC         1$
    ; HANDLE THE ERROR WHOSE CODE IS IN THE B REGISTER.
1$:
    ; CALL SUCCESSFUL AND X HAS THE TAG OF THE CELL.



       ____________
5.1.5  MEMORY USAGE

     In the following description refer to chapter 6 for the  addresses  of
the variables described.

     The six words of memory storage labelled UTW_S0 to UTW_S5 are a set of
scratch  variables used by the operating system which any service may trash
as required.  Thus no values can be held in these words while making a call
to  an  operating  system  service,  although  they may be used for storing
intermediate values between calls to the operating system.

     The seven words of memory storage labelled UTW_R0 to UTW_R6 are a  set
of  fixed  variables  which are not trashed by the operating system service
routines.  The service routines actually use  these  variables  but  always
push  their  contents  on  the  stack  before  use and then recover them by
popping them off the stack  again.   Application  programs  may  use  these
variables as long as they maintain their integrity by pushing and popping.

     As a code saving device there is a system  service  to  push  and  pop
these variables as follows:

    OS          BT$PPRG                 ; PUSH UTW_R0
    .BYTE       1                       ; INSTRUCTION BYTE TO BT$PPRG
    ; CAN NOW USE UTW_R0
    OS          BT$PPRG                 ; POP UTW_R0
    .BYTE       $81                     ; INSTRUCTION BYTE TO BT$PPRG


     The byte following the call to BT$PPRG instructs the  service  whether
to  push or pop the variables from the stack and which variables to push or
pop.  The format of the byte is as follows:

    BIT 7 - If set then pop the variables else push the variables
    BIT 6 - If set then push or pop UTW_R6
    BIT 5 - If set then push or pop UTW_R5
    BIT 4 - If set then push or pop UTW_R4
    BIT 3 - If set then push or pop UTW_R3
    BIT 2 - If set then push or pop UTW_R2
    BIT 1 - If set then push or pop UTW_R1
    BIT 0 - If set then push or pop UTW_R0


     Thus if the byte value is $5 then UTW_R2 and UTW_R0 will be pushed.

     When pushing, the higher address variables are pushed first  and  when
popping,  the lower address variables are popped first.  Thus if UTW_R5 and
UTW_R2 are pushed and UTW_R2 and UTW_R1 are popped then UTW_R1 will get the
old value of UTW_R2 and UTW_R2 will get the old value of UTW_R5.



       ___________________________
5.1.6  SYSTEM CONSTANTS AND MACROS

     The following is a set of useful constants  and  macros  used  in  the
description of the system services and in the examples.
;
; MBSET MACRO
; ===========
;
        .MACRO  MBSET   MASK,ADDR
                OIM     #MASK,ADDR
        .ENDM   MBSET
;
; MBCLR MACRO
; ===========
;
        .MACRO  MBCLR   MASK,ADDR
                AIM     #XFF-<MASK>,ADDR
        .ENDM   MBCLR
;
; MBTGL MACRO
; ===========
;
        .MACRO  MBTGL   MASK,ADDR
                EIM     #MASK,ADDR
        .ENDM
;
; MBTST MACRO
; ===========
;
        .MACRO  MBTST   MASK,ADDR
                TIM     #MASK,ADDR
        .ENDM
;
; CONSTANTS USED BY MPSH AND MPUL MACROS
; ======================================
;
$mtr0   equ     1
$mtr1   equ     2
$mtr2   equ     4
$mtr3   equ     8
$mtr4   equ     16
$mtr5   equ     32
$mtr6   equ     64
;
; THE MPSH MACRO
; ==============
;
        .MACRO  MPSH    P0,P1,P2,P3,P4,P5,P6
        $MSK    EQU     0
        .IF     NB <P0>
        $MSK    EQU     $MSK ! $MT'P0
        .IF     NB <P1>
        $MSK    EQU     $MSK ! $MT'P1
        .IF     NB <P2>
        $MSK    EQU     $MSK ! $MT'P2
        .IF     NB <P3>
        $MSK    EQU     $MSK ! $MT'P3
        .IF     NB <P4>
        $MSK    EQU     $MSK ! $MT'P4
        .IF     NB <P5>
        $MSK    EQU     $MSK ! $MT'P5
        .IF     NB <P6>
        $MSK    EQU     $MSK ! $MT'P6
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        OS      BT$PPRG
        FCB     $MSK
        .ENDM   MPSH
;
; THE MPUL MACRO
; ==============
;
        .MACRO  MPUL    P0,P1,P2,P3,P4,P5,P6
        $MSK    EQU     0
        .IF     NB <P0>
        $MSK    EQU     $MSK ! $MT'P0
        .IF     NB <P1>
        $MSK    EQU     $MSK ! $MT'P1
        .IF     NB <P2>
        $MSK    EQU     $MSK ! $MT'P2
        .IF     NB <P3>
        $MSK    EQU     $MSK ! $MT'P3
        .IF     NB <P4>
        $MSK    EQU     $MSK ! $MT'P4
        .IF     NB <P5>
        $MSK    EQU     $MSK ! $MT'P5
        .IF     NB <P6>
        $MSK    EQU     $MSK ! $MT'P6
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        .ENDC
        OS      BT$PPRG
        FCB     X80 ! $MSK
        .ENDM MPUL
;
; ZERO PAGE PORTS
; ===============
;
POB_DDR2   EQU  $01     ; PORT 2 DATA DIRECTION REGISTER
POB_PORT2  EQU  $03     ; PORT 2 DATA REGISTER
POB_TCSR1  EQU  $08     ; TIMER CONTROL STATUS REGISTER 1
POW_FRC    EQU  $09     ; FREE RUNNING COUNTER
POW_OCR1   EQU  $0B     ; OUTPUT COMPARE REGISTER 1
POB_TCSR2  EQU  $0F     ; TIMER 2 CONTROL/STATUS REGISTER
POB_RMCR   EQU  $10     ; RATE MODE CONTROL REGISTER
POB_TRCSR  EQU  $11     ; TX/RX CONTROL STATUS REGISTER
POB_RDR    EQU  $12     ; RECEIVE DATA REGISTER
POB_TDR    EQU  $13     ; TRANSMIT DATA REGISTER
POB_RCR    EQU  $14     ; RAM/PORT 5 CONTROL REGISTER
POB_PORT5  EQU  $15     ; PORT 5 DATA REGISTER
POB_DDR6   EQU  $16     ; PORT 6 DATA DIRECTION REGISTER
POB_PORT6  EQU  $17     ; PORT 6 DATA REGISTER
POB_TCSR3  EQU  $1B     ; TIMER 3 CONTROL/STATUS REGISTER
POB_TCONR  EQU  $1C     ; TIMER CONSTANT REGISTER
;
; SEMI-CUSTOM CHIP ADDRESSES
; ==========================
;
SCA_LCDCONTROL   EQU    $0180   ; LCD CONTROL REGISTER
SCA_LCDDATA      EQU    $0181   ; LCD DATA REGISTER
SCA_SWITCHOFF    EQU    $01C0   ; SWITCH OFF
SCA_PULSEENABLE  EQU    $0200   ; PULSE ENABLE
SCA_PULSEDISABLE EQU    $0240   ; PULSE DISABLE
SCA_ALARMHIGH    EQU    $0280   ; BUZZER ON
SCA_ALARMLOW     EQU    $02C0   ; BUZZER OFF
SCA_COUNTERRESET EQU    $0300   ; SET COUNTER TO 0
SCA_COUNTERCLOCK EQU    $0340   ; CLOCK COUNTER ONCE
SCA_NMIMPU       EQU    $0380   ; ENABLE NMI TO PROCESSOR
SCA_NMICOUNTER   EQU    $03C0   ; ENABLE NMI TO COUNTER
;
; PORT 5 BITS
; ===========
;
ONCLR      EQU  $80     ; ON/CLEAR LINE
ACOUT      EQU  $02     ; ACOUT LINE
LOWBATTERY EQU  $01     ; LOW BATTERY LINE
;
; PORT 6 BITS
; ===========
;
PACON   EQU     $80     ; PACK VCC ENABLE SIGNAL
CS3     EQU     $40     ; CHIP SELECT 3 SIGNAL
CS2     EQU     $20     ; CHIP SELECT 2 SIGNAL
CS1     EQU     $10     ; CHIP SELECT 1 SIGNAL
OE      EQU     $08     ; OUTPUT ENABLE SIGNAL
PGM     EQU     $04     ; PROGRAM SIGNAL
MR      EQU     $02     ; MASTER RESET SIGNAL
CLK     EQU     $01     ; CLOCK SIGNAL
;
; TCSR1 BITS
; ==========
;
EOCI1   EQU     $08     ; TIMER 1 INTERRUPT ENABLE
;
; KBB_STAT BITS
; =============
;
KY_SHFT EQU     $80             ; SHIFT
KY_NUMB EQU     $40             ; NUMERIC LOCK
KY_CPNM EQU     $02             ; CAPS / NUMB FLAG
KY_CAPS EQU     $01             ; CAPS LOCK
;
; PACK CONTROL DELAYS
; ===================
;
PACONDEL     EQU        11520           ; FOR 50MS DELAY
VPPONDEL     EQU        2304            ; FOR 10MS DELAY
VPPOFFDEL    EQU        46080           ; FOR 200MS DELAY
PK_OVERBLOW  EQU        5               ; 5*X OVERBLOW
;
; MISCELLANEOUS CONSTANTS
; =======================
;
RAMBASE         EQU     $2000           ; MACHINE RAM BASE
RAMFREE         EQU     BTT_RAMF        ; FIRST FREE RAM BYTE
MACHINE_STACK   EQU     $0100           ; SIZE OF MACHINE STACK
MINEVL_STACK    EQU     $0100           ; MIN. SIZE OF EVALUATOR STACK
ALLCELLS        EQU     32              ; NUMBER OF ALLOCATOR CELLS
PERMCELL        EQU     0               ; PERMANENT CELL
MENUCELL        EQU     1               ; TOP LEVEL MENU CELL
DIRYCELL        EQU     2               ; DIARY CELL
TEXTCELL        EQU     3               ; LANGUAGE TEXT CELL
SYMBCELL        EQU     4               ; SYMBOL TABLE CELL
GLOBCELL        EQU     5               ; GLOBAL RECORD CELL
OCODCELL        EQU     6               ; QCODE OUTPUT CELL
FSY1CELL        EQU     7               ; FIELD NAME SYMBOL TABLE 1
FSY2CELL        EQU     8               ; FIELD NAME SYMBOL TABLE 2
FSY3CELL        EQU     9               ; FIELD NAME SYMBOL TABLE 3
FSY4CELL        EQU     10              ; FIELD NAME SYMBOL TABLE 4
FBF1CELL        EQU     11              ; FIELD BUFFER CELL 1
FBF2CELL        EQU     12              ; FIELD BUFFER CELL 2
FBF3CELL        EQU     13              ; FIELD BUFFER CELL 3
FBF4CELL        EQU     14              ; FIELD BUFFER CELL 4
DATACELL        EQU     15              ; DATABASE CELL
PREALLOC        EQU     16              ; NUMBER OF CELLS TO PREALLOCATE
SWIDTH          EQU     $10             ; SCREEN WIDTH
CURS_ON         EQU     $80             ; CURSOR ON FLAG
CURS_OFF        EQU     $00             ; CURSOR OFF
CURSOR_BLOCK    EQU     $00             ; CURSOR IN BLOCK FORM
CURSOR_LINE     EQU     $01             ; CURSOR IN LINE FORM
TIMEOUT         EQU     300             ; AUTOMATIC TIMEOUT IN 5 MINS
BSIZE           EQU     <256+64>        ; RTT_BF BUFFER SIZE
FSIZE           EQU     32              ; RTT_FF BUFFER SIZE
DELIM           EQU     9               ; BUFFER DELIMITER
KEY_TIME        EQU     $b3dd           ; GIVES 50.000MS KEY POLLING
KEY_DELAY       EQU     14              ; DELAY BEFORE KEY REPEAT
KEY_REPEAT      EQU     0               ; RATE OF KEY REPEAT 0=FASTEST
KEY_CLICK       EQU     1               ; LENGTH OF KEY CLICK
TYPEAHEAD       EQU     16              ; 16 CHARACTER TYPE AHEAD
HDELAY          EQU     4               ; HORIZONTAL SCROLLING DELAY
VDELAY          EQU     10              ; VERTICAL SCROLLING DELAY
REGSIZE         EQU     32              ; NUMBER OF TABLE REGISTERS
REGBASE         EQU     <256-REGSIZE>   ; FIRST REGISTER NUMBER
STACKSIZE       EQU     32              ; TABLE STACK SIZE
;
; SYMBOLIC KEY CODE NAMES
; ========================
;
K_AC            EQU     1               ; ON/CLEAR KEY
K_MODE          EQU     2               ; MODE KEY
K_UP            EQU     3               ; UP ARROW
K_DOWN          EQU     4               ; DOWN ARROW
K_LEFT          EQU     5               ; LEFT ARROW
K_RGHT          EQU     6               ; RIGHT ARROW
K_DELR          EQU     7               ; DELETE RIGHT KEY
K_DEL           EQU     8               ; DELETE KEY
K_EXE           EQU     13              ; EXECUTE KEY
;
; SCREEN DISPLAY CONTROL CODES
; ============================
;
D_BS            EQU     8               ; BACK SPACE
D_HT            EQU     9               ; NEAREST POSITION MODULO 8
D_LF            EQU     10              ; LINE FEED
D_HM            EQU     11              ; POSITION CURSOR TOP LEFT
D_FF            EQU     12              ; CLEAR ENTIRE DISPLAY
D_CR            EQU     13              ; GOTO START OF LINE
D_CT            EQU     14              ; CLEAR TOP LINE
D_CB            EQU     15              ; CLEAR BOTTOM LINE
D_BL            EQU     16              ; BELL
D_RE            EQU     17              ; REFRESH BOTH LINES
D_TR            EQU     18              ; REFRESH TOP LINE
D_BR            EQU     19              ; REFRESH BOTTOM LINE
;
; SLOT SYMBOLIC NAME
; ==================
;
PAKA            EQU     0               ; RAM DATA PACK
PAKB            EQU     1               ; FIRST PACK SLOT
PAKC            EQU     2               ; SECOND PACK SLOT
PAKD            EQU     3               ; TOP SLOT
;
; DATAPACK FIRST BYTE BITS
; ========================
;
EPROM           EQU     $02             ; SET IF EPROM PACK (NOT RAM PACK)
PGCPK           EQU     $04             ; SET IF PACK WITH PAGE COUNTER
RDWRT           EQU     $08             ; CLEAR IF PACK WRITE PROTECTED
NOBOOT          EQU     $10             ; CLEAR IF PACK BOOTABLE
COPYPK          EQU     $20             ; SET IF PACK COPYABLE
NYIMPL          EQU     $40             ; SET FOR FUTURE EXPANSION
MK1PAK          EQU     $80             ; SET IF MARK I PACK
;
; FILING SYSTEM
; =============
;
MAXFILE         EQU     4               ; MAXIMUM NUMBER OF OPEN FILES
BBODTYP         EQU     $80             ; BLOCK BODY RECORDS
NAMETYP         EQU     $81             ; RECORD TYPE FOR FILE NAMES
BDIATYP         EQU     $82             ; BLOCK NAME TYPE FOR DIARY
BLANTYP         EQU     $83             ; BLOCK NAME TYPE FOR OPL
FRECTYP         EQU     $91             ; FIRST FREE RECORD TYPE
NAMELEN         EQU     8               ; MAX LEN OF A FILE NAME
TLRECT          EQU     <FRECTYP-1>     ; RECORD TYPE FOR MAIN



       _____________
5.1.7  ERROR NUMBERS

     Included below are  all  the  symbolic  names  of  the  error  numbers
returned by the operating system services.

     These error numbers are always returned in the  B  register  after  an
operating system service has signaled an error by returning with the carry
flag set.
ER_AL_NC EQU    255     ; NO MORE ALLOCATOR CELLS
ER_AL_NR EQU    254     ; NO MORE ROOM
ER_MT_EX EQU    253     ; EXPONENT OVERFLOW (OR UNDERFLOW)
ER_MT_IS EQU    252     ; CONVERSION FROM STRING TO NUMERIC FAILED
ER_MT_DI EQU    251     ; DIVIDE BY ZERO
ER_MT_FL EQU    250     ; CONVERSION FROM NUMERIC TO STRING FAILED
ER_IM_OV EQU    249     ; BCD STACK OVERFLOW
ER_IM_UN EQU    248     ; BCD STACK UNDERFLOW
ER_FN_BA EQU    247     ; BAD ARGUMENT IN FUNCTION CALL
ER_PK_NP EQU    246     ; NO PACK IN SLOT
ER_PK_DE EQU    245     ; DATAPACK ERROR (WRITE ERROR)
ER_PK_RO EQU    244     ; ATTEMPTED WRITE TO READ ONLY PACK
ER_PK_DV EQU    243     ; BAD DEVICE NAME
ER_PK_CH EQU    242     ; PACK CHANGED
ER_PK_NB EQU    241     ; PACK NOT BLANK
ER_PK_IV EQU    240     ; UNKNOWN PACK TYPE
ER_FL_PF EQU    239     ; PACK FULL
ER_FL_EF EQU    238     ; END OF FILE
ER_FL_BR EQU    237     ; BAD RECORD TYPE
ER_FL_BN EQU    236     ; BAD FILE NAME
ER_FL_EX EQU    235     ; FILE ALREADY EXISTS
ER_FL_NX EQU    234     ; FILE DOES NOT EXIST
ER_FL_DF EQU    233     ; DIRECTORY FULL
ER_FL_CY EQU    232     ; PACK NOT COPYABLE
ER_DV_CA EQU    231     ; INVALID DEVICE CALL
ER_DV_NP EQU    230     ; DEVICE NOT PRESENT
ER_DV_CS EQU    229     ; CHECKSUM ERROR
ER_EX_SY EQU    228     ; SYNTAX ERROR
ER_EX_MM EQU    227     ; MISMATCHED BRACKETS
ER_EX_FA EQU    226     ; WRONG NUMBER OF FUNCTION ARGS
ER_EX_AR EQU    225     ; SUBSCRIPT OR DIMENSION ERROR
ER_EX_TV EQU    224     ; TYPE VIOLATION
ER_LX_ID EQU    223     ; IDENTIFIER TOO LONG
ER_LX_FV EQU    222     ; BAD FIELD VARIABLE NAME
ER_LX_MQ EQU    221     ; UNMATCHED QUOTES IN STRING
ER_LX_ST EQU    220     ; STRING TOO LONG
ER_LX_US EQU    219     ; UNRECOGNISED SYMBOL
ER_LX_NM EQU    218     ; NON-VALID NUMERIC FORMAT
ER_TR_PC EQU    217     ; MISSING PROCEDURE DECLARATION
ER_TR_DC EQU    216     ; ILLEGAL DECLARATION
ER_TR_IN EQU    215     ; NON-INTEGER DIMENSION
ER_TR_DD EQU    214     ; NAME ALREADY DECLARED
ER_TR_ST EQU    213     ; STRUCTURE ERROR
ER_TR_ND EQU    212     ; NESTING TOO DEEP
ER_TR_NL EQU    211     ; LABEL REQUIRED
ER_TR_CM EQU    210     ; MISSING COMMA
ER_TR_BL EQU    209     ; BAD LOGICAL FILE NAME
ER_TR_PA EQU    208     ; ARGUMENTS MAY NOT BE TARGET OF ASSIGN
ER_TR_FL EQU    207     ; TOO MANY FIELDS
ER_RT_BK EQU    206     ; BREAK KEY
ER_RT_NP EQU    205     ; WRONG NUMBER OF PARAMETERS
ER_RT_UE EQU    204     ; UNDEFINED EXTERNAL
ER_RT_PN EQU    203     ; PROCEDURE NOT FOUND
ER_RT_ME EQU    202     ; MENU ERROR
ER_RT_NF EQU    201     ; FIELD NOT FOUND
ER_PK_BR EQU    200     ; PACK BAD READ ERROR
ER_RT_FO EQU    199     ; FILE ALREADY OPEN (OPEN/DELETE)
ER_RT_RB EQU    198     ; RECORD TOO BIG
ER_LG_BN EQU    197     ; BAD PROCEDURE NAME
ER_RT_FC EQU    196     ; FILE NOT OPEN (CLOSE)
ER_RT_IO EQU    195     ; INTEGER OVERFLOW
ER_GN_BL EQU    194     ; BATTERY TOO LOW
ER_GN_RF EQU    193     ; DEVICE READ FAIL
ER_GN_WF EQU    192     ; DEVICE WRITE FAIL



       ______________
5.1.8  VECTOR NUMBERS

     Included below are all the operating system service names and  numbers
which may be used to set up an include file for machine code applications.

    AL$FREE 000  AL$GRAB 001  AL$GROW 002  AL$REPL 003  AL$SHNK 004
    AL$SIZE 005  AL$ZERO 006  BT$NMDN 007  BT$NMEN 008  BT$NOF  009
    BT$NON  010  BT$PPRG 011  BT$SWOF 012  BZ$ALRM 013  BZ$BELL 014
    BZ$TONE 015  DP$EMIT 016  DP$PRNT 017  DP$REST 018  DP$SAVE 019
    DP$STAT 020  DP$VIEW 021  DP$WRDY 022  DV$BOOT 023  DV$CLER 024
    DV$LKUP 025  DV$LOAD 026  DV$VECT 027  ED$EDIT 028  ED$EPOS 029
    ED$VIEW 030  ER$LKUP 031  ER$MESS 032  FL$BACK 033  FL$BCAT 034
    FL$BDEL 035  FL$BOPN 036  FL$BSAV 037  FL$CATL 038  FL$COPY 039
    FL$CRET 040  FL$DELN 041  FL$ERAS 042  FL$FFND 043  FL$FIND 044
    FL$FREC 045  FL$NEXT 046  FL$OPEN 047  FL$PARS 048  FL$READ 049
    FL$RECT 050  FL$RENM 051  FL$RSET 052  FL$SETP 053  FL$SIZE 054
    FL$WRIT 055  FN$ATAN 056  FN$COS  057  FN$EXP  058  FN$LN   059
    FN$LOG  060  FN$POWR 061  FN$RND  062  FN$SIN  063  FN$SQRT 064
    FN$TAN  065  IT$GVAL 066  IT$RADD 067  IT$STRT 068  IT$TADD 069
    KB$BREK 070  KB$FLSH 071  KB$GETK 072  KB$INIT 073  KB$STAT 074
    KB$TEST 075  KB$UGET 076  LG$NEWP 077  LG$RLED 078  LN$STRT 079
    MN$DISP 080  MT$BTOF 081  MT$FADD 082  MT$FBDC 083  MT$FBEX 084
    MT$FBGN 085  MT$FBIN 086  MT$FDIV 087  MT$FMUL 088  MT$FNGT 089
    MT$FSUB 090  PK$PKOF 091  PK$QADD 092  PK$RBYT 093  PK$READ 094
    PK$RWRD 095  PK$SADD 096  PK$SAVE 097  PK$SETP 098  PK$SKIP 099
    RM$RUNP 100  TL$ADDI 101  TL$CPYX 102  TL$DELI 103  TL$XXMD 104
    TM$DAYV 105  TM$TGET 106  TM$UPDT 107  TM$WAIT 108  UT$CPYB 109
    UT$DDSP 110  UT$DISP 111  UT$ENTR 112  UT$FILL 113  UT$ICPB 114
    UT$ISBF 115  UT$LEAV 116  UT$SDIV 117  UT$SMUL 118  UT$SPLT 119
    UT$UDIV 120  UT$UMUL 121  UT$UTOB 122  UT$XCAT 123  UT$XTOB 124
    UT$YSNO 125
    UT$CDSP 126  ;AVAILABLE ON VERSION 2.5 AND ABOVE ONLY
    TL$RSTR 127  ;AVAILABLE ON VERSION 2.7 AND ABOVE ONLY



     _______________
5.2  SYSTEM VERSIONS

     There are 3 machine variants supplied by PSION differing only  in  the
amount of external RAM memory available.

     1.  CM - 8K RAM

     2.  XP - 16K RAM

     3.  LA - 31K RAM


     The LA and XP variants can  also  be  produced  with  just  a  numeric
keyboard  which are additionally labelled as POS200 machines, so that there
exist two other machines known as the XP POS200 and  the  LA  POS200.   The
only differences between the 5 machines lie in the operating system portion
of the machine and as such there are 5 operating system variants:

     1.  CM/OS - CM machine operating system.

     2.  XP/OS - XP machine operating system.

     3.  XP2/OS - XP POS 200 machine operating system.

     4.  LA/OS - LA machine operating system.

     5.  LA2/OS - LA POS 200 machine operating system.


     The difference between the normal operating system  and  the  POS  200
variant  is  in the handling of the top level.  The normal operating system
enters the top level menu and  then  dispatches  to  the  various  services
available, while the POS 200 does the following:

     1.  Boot all devices.

     2.  Scan all devices for an OPL procedure called BOOT.

     3.  If the procedure is not found then display INSERT PACK and  switch
         off after 1 second.

     4.  If the procedure is found then run the procedure.

     5.  Repeat the above steps.


     Also,  the  POS200  variants   support   the   numeric-only   keyboard
automatically.

     In order to allow the machine type to be determined  as  well  as  the
software  revision  level of the ROM, two bytes are permanently reserved in
the ROM at the following addresses.

    $FFE8 - Machine type.
    $FFE9 - Software revision level number.



       _____
5.2.1  CM/OS

     $FFE8 = $00

     The CM/OS is the base operating system from which all other  operating
system  variants  are  derived.  As such any software written to run on the
CM/OS is guaranteed to run on all  other  operating  system  variants.   In
other words software is upwardly compatible between the operating systems.



       ________________
5.2.2  XP/OS AND XP2/OS


    $FFE8 = $01 XP/OS  - XP machine.
    $FFE8 = $81 XP2/OS - XP POS 200 machine.


     As for the CM/OS but will support the following extra facilities:

     1.  128K DATAPACKS

     2.  RAM DATAPACKS

     3.  BAR CODE READERS

     4.  SWIPE READERS




       ________________
5.2.3  LA/OS AND LA2/OS


    $FFE8 = $02 LA/OS  - LA machine.
    $FFE8 = $82 LA2/OS - LA POS 200 machine.


     As for the XP/OS with the  exception  that  the  memory  allocator  is
completely  different.  This is because the system variables are located at
$2000 in the CM/OS and XP/OS as external RAM only starts at  this  address.
However  in  the LA machines external RAM starts at address $400.  In order
to keep the operating systems compatible the  system  variables  are  still
located  at address $2000 in the LA machines and as such the free RAM is in
two sections, between $400 and $2000 and above the  system  variables.   In
order  to  allow the operating system to use the extra 7K of RAM the memory
allocator effectively joins these two discontinuous areas of RAM  together.
See the chapter 6 for more information.



     ________
5.3  POWER UP

     The machine can be switched on in 3 different ways.

     1.  By pressing the ON/CLEAR key.

     2.  By the clock counter expiring in the semi-custom chip.

     3.  By asserting the ON line from the top slot.


     On power up the program counter is  loaded  from  the  system  restart
vector  at  address  $FFFE in the operating system ROM.  The system restart
vector is set to address $8000 in all versions  of  the  operating  system,
which is the base address of the operating system ROM.  The restart code is
then executed in the following sequence.

     1.  Zero page RAM is enabled by setting the RAME bit in PORT 5 of  the
         processor.

     2.  The machine stack is initialised temporarily to the  top  of  zero
         page RAM, i.e.  at address $FF.

     3.  The LCD display is cleared.

     4.  The control lines to the datapack bus are initialised to  a  known
         state.


     The next task performed  by  the  operating  system  is  to  determine
whether a warm or cold start is required.  Essentially a cold start is when
the machine is starting up for the first time after a power failure and  as
such  all  operating system variables must be initialised.  A warm start is
when the machine only needs to carry on from when it was powered  down,  as
all RAM values are still valid.

     The Hitachi HD6303X microprocessor has an internal flag  to  determine
whether power to the internal RAM in the processor has failed at any stage.
This flag is the top bit in PORT 5.  If the flag is clear then power to the
internal  RAM has failed at some stage and so a cold start is required.  If
the flag is still set then the internal RAM is still intact and so  a  warm
start  is  required.   As the external RAM is on the same power rail as the
processor the above flag also  serves  to  describe  the  validity  of  the
external RAM.



       __________
5.3.1  COLD START

     On  executing  a  cold  start  the  machine  performs  the   following
procedures:

     1.  Perform a simple RAM test on the external RAM.

     2.  Determine the last address in the external RAM.

     3.  Check that this address is  valid  for  the  three  memory  models
         available, i.e.  $3fff, $5fff or $7fff.

     4.  If the value does not correspond to one of the valid  values  then
         the  RAM  must be faulty, so the buzzer is sounded and the machine
         powered down.

     5.  Use the last address of valid RAM plus 1 to initialise BTA_RTOP.

     6.  Set the machine stack address to BTA_RTOP.

     7.  Subtract 256 from BTA_RTOP and use the value to initialise  RTA_SP
         and BTA_SBAS.  This leaves 256 bytes for the machine stack.

     8.  Initialise all soft vectors and all operating system variables.

     9.  Enable NMI interrupts to the processor.

    10.  Start the timer to provide keyboard scan interrupts.

    11.  Test that the battery voltage is over 5 volts.  If it is not  then
         display  low battery message for 4 seconds and then switch off the
         machine.  Low battery is a hardware flag in POB_PORT5 and  can  be
         tested as follows.

                LDA             A,POB_PORT5
                ROR             A
                BCC             1$
                ; BATTERY IS LOW
             1$:
                ; BATTERY IS OK

    12.  Boot any devices.

    13.  Start at the top level menu.




       __________
5.3.2  WARM START

     On deciding that  a  warm  start  is  required  the  operating  system
performs the following code:

        LDS     BTA_SAVSTACK
        LDX     BTA_WRM
        JMP     0,X

     The power off service BT$SWOF stores the stack pointer in BTA_SAVSTACK
before  switching  off  the machine to enable the machine to restart at the
same place it was at when the machine was switched  off.   With  the  stack
restored  to  the  value  that  it  had  in BT$SWOF, an "RTS" will continue
execution after the call to BT$SWOF.  Next the vector for warm starting  is
used  to  jump  to  a  warm  start  routine.  The warm start routine may be
replaced by another routine but the operating  system  warm  start  routine
should  be called as well.  If it is not the operating system will not work
correctly.  See section 5.6 on replacing vectored routines.

     The system warm start routine performs the following actions:

     1.  Switch non-maskable interrupts (NMI) on to the processor.

              This is done by testing the ADDRESS SCA_NMIMPU with

              TST               SCA_NMIMPU

     2.  Wait for the first NMI to occur.

              This is necessary as on each switch-on the clock  counter  in
         the  semi  custom chip gains a second and so the first NMI must be
         ignored.  See chapter 2 section 2.6 for further details.

     3.  Test the hardware flag ACOUT in POB_PORT5.

              If the flag is true then the counter has expired and the time
         needs updating as follows:

         1.  Update the system clock by the length of time the machine  has
             been switched off for.

         2.  Determine whether an alarm is due currently and if so carry on
             with  the  power-on sequence.  If not then just switch off the
             machine again.


              Otherwise the machine was switched on with the  ON/CLEAR  key
         or by an external interface.  Update the time the machine has been
         switched off for.

     4.  Restore the display to its state before power down.

     5.  Set the ALARM_TO_DO flag so that any alarms will be serviced.

     6.  Reset the AUTO_SWITCH_OFF countdown and check  that  it's  greater
         than 15 seconds.  If it is not then make it 15 seconds.

     7.  Check for low battery as in warm starting.

     8.  Restore the interrupt status and  the  value  in  TIMER  1  STATUS
         CONTROL REGISTER (TSCR1) which were saved by the BT$SWOF service.

     9.  Wait for the ON/CLEAR key to be released.

    10.  Restore the USER-DEFINED GRAPHICS as saved by the BT$SWOF service.

    11.  Flush the keyboard buffer and restart keyboard scan interrupts.

    12.  Execute a return instruction which  resumes  execution  after  the
         call to the BT$SWOF service.




     __________
5.4  POWER DOWN

     The machine can be switched off by  calling  the  POWER  DOWN  service
routine BT$SWOF.  This routine is vectored through BTA_SOF as follows:

        STS     BTA_SAVSTACK
        LDX     BTA_SOF
        JMP     0,X


     The power down routine may be replaced  by  another  routine  but  the
operating system power down routine should be called as well.  If it is not
the operating system will not work correctly.  See section 5.6 on replacing
vectored routines.

     The system power down service performs the following steps:

     1.  Save the current  value  of  the  status  flag,  to  preserve  the
         interrupt status.

     2.  Save the value in the TIMER 1 STATUS CONTROL REGISTER (TSCR1).

     3.  Disable interrupts.

     4.  Clear the LCD display.

     5.  Save the current values of the USER DEFINED GRAPHICS in the LCD.

     6.  Switch off the interface slots.

     7.  Reset the COUNTER to 0.

     8.  Check whether any alarms are due to run in the next 34 minutes and
         8 seconds.  If so, adjust the counter so that the machine is woken
         up in time to service the  alarm.   See  section  2.6.2  for  more
         information.

     9.  Switch non-maskable interrupts to the COUNTER.

    10.  Disable the internal RAM by clearing the RAME bit in POB_RCR.

    11.  Test the address SCA_SWITCHOFF to put  the  processor  in  standby
         mode.




     __________
5.5  INTERRUPTS

     The operating system uses four  of  the  ten  hardware  interrupts  to
perform  various  services.   The  remainder  are  just  directed  to a RTI
instruction.  However, all interrupts are vectored through RAM so that they
may  be  intercepted  or replaced in total.  For the interrupts used by the
operating system it is recommended that the interrupt only  be  intercepted
and  not  be  replaced if it is required that the operating system performs
according to specification.



       _______________________
5.5.1  NON-MASKABLE INTERRUPTS

     The semi-custom chip will deliver an NMI to the processor exactly once
every  second  to  provide  an  accurate system clock, provided the address
SCA_NMIMPU has been accessed.  The NMIs to the processor can be disabled by
accessing the address SCA_NMICOUNTER.  Note that this is an unusual feature
since NMIs, as their name implies, cannot normally be disabled.

     The NMI service routine performs the following actions:

     1.  Clear the flag BTB_NMFL.

              This is to allow code to detect that an NMI has  occurred  as
         follows:

                INC     BTB_NMFL
             1$:
                SLP                     ; Go to sleep until an interrupt
                TST     BTB_NMFL        ; Test NMI flag
                BNE     1$              ; Still set - so wrong interrupt
                ; NMI interrupt occurred.


     2.  Test the BTB_IGNM (ignore NMI flag, set on warm starting)

              If it  is  zero  then  set  the  flag  and  return  from  the
         interrupt.

     3.  Update the system time by one second.

     4.  Check whether the seconds count is exactly  zero,  i.e.   a  whole
         minute.

              If it is then check the alarms enabled flag AMB_EI.

              If it is set then set AMB_DOIT which will trigger a  scan  of
         the  alarms  pending  lists  at  the next TIMER 1 interrupt.  Thus
         alarms are scanned only every minute and are under control of  the
         processor interrupt flag.  See chapter 2 for more information.


     5.  Check the auto switch off flag TMB_SWOF.

              If it's set then decrement the time out count in TMW_TOUT  if
         it is not already zero.

     6.  Return from the interrupt.




       _________________________
5.5.2  TIMER 1 COMPARE INTERRUPT

     The timer 1 compare interrupt is used to scan the  keyboard  to  allow
keyboard  buffering  and  to  provide  a timing service.  This interrupt is
referred to in the documentation  as  the  KEYBOARD  INTERRUPT  (KI).   The
interrupt  is  generated  every  time  the free running counter matches the
count in the timer 1 compare register.  As  the  free  running  counter  is
being  clocked  by the system clock of 921600 HZ, extremely accurate timing
can be performed using this interrupt.   The  time  between  interrupts  is
controlled  by  the variable KBW_TDEL which is initialised on cold start to
be $B3DD.  This value  makes  the  KI  interrupt  occur  exactly  every  50
milliseconds  and  is  used  extensively by the operating system for timing
purposes.  The value in KBW_TDEL can be changed, but all system timing will
be  destroyed  as  a  result  and  the operating system may fail to perform
correctly.

     The KI service routine performs the following steps:

     1.  Reset the free running counter to zero.

     2.  Set the timer 1 output compare register to the value in KBW_TDEL.

     3.  Check the alarm service required flag AMB_DOIT.

              If it is set then run the alarm service and  clear  the  flag
         AMB_DOIT.

     4.  Increment the frame counter TMW_FRAM.

     5.  Decrement the word DPW_REDY if it's not already zero.

              This flag is used to perform system timing for the  operating
         system.   If  a  delay  of 150 milliseconds were required then the
         following code could be used to achieve that delay:

                LDX     #3        ; Three KI interrupts at 50 ms each
                STX     DPW_REDY:
             1$:
                SLP               ; Wait for interrupt
                LDD     DPW_REDY: ; See if decremented to zero yet
                BNE     1$
                ; 150 ms now elapsed.


     6.  Poll the keyboard.  See section 7.3.2 for more information.




       __________________
5.5.3  SOFTWARE INTERRUPT

     This interrupt is used to provide the interface  between  applications
and the operating system.  When a SWI instruction is executed the following
code is executed:

        LDX     BTA_SWI
        JMP     0,X


     The SWI service  routine  provided  by  the  operating  system  is  as
follows:

        PUL     A
        STA     A,BTB_4DONTUSE          ;SAVE STATUS FLAG
        PUL     B
        PUL     A
        STD     BTW_1DONTUSE            ;SAVE THE D REGISTER
        PULX
        STX     BTW_2DONTUSE            ;SAVE THE X REGISTER
        PULX                            ;GET THE ADDRESS OF THE BYTE
        LDA     B,0,X                   ;FOLLOWING THE SWI INSTRUCTION
        INX                             ;INCREMENT TO SKIP OVER THE BYTE
        PSHX                            ;PUSH BACK AS RETURN ADDRESS
        LDX     BTA_VECT                ;GET THE VECTOR TABLE ADDRESS
        ABX                             ;DOUBLE THE VECTOR NUMBER AND
        ABX                             ;ADD TO VECTOR TABLE
        LDX     0,X                     ;GET ADDRESS OF ROUTINE
        PSHX                            ;SAVE ON STACK FOR DUMMY RETURN
        LDX     BTW_2DONTUSE            ;RESTORE X REGISTER
        LDD     BTW_1DONTUSE            ;RESTORE D REGISTER
        PSH     A                       ;SAVE A REGISTER
        LDA     A,BTB_4DONTUSE          ;GET STATUS FLAGS
        TAP                             ;RESTORE STATUS FLAGS
        PUL     A                       ;RESTORE A REGISTER
        RTS                             ;JUMP TO REQUIRED ROUTINE



       ______________
5.5.4  TRAP INTERRUPT

     The operating system routine  to  handle  the  trap  interrupt  simply
clears  the LCD display and displays "TRAP" on the screen until the battery
is removed and the machine is COLD started again.  It is intended that this
trap  remain free for use with a debugger at some time in the future and as
such should not be used.



     _______
5.6  VECTORS

     In order to provide  flexibility  in  the  operating  system  all  the
hardware  interrupts  are  vectored through RAM vectors so that they may be
intercepted or even replaced.  In addition a  number  of  operating  system
services  are  provided  through  vectors  as  well  so  that  they  may be
intercepted or replaced more easily than intercepting the SWI interrupt.

     If the  operating  system  is  using  an  interrupt,  it  is  strongly
recommended  that  the  interrupt  is  just  intercepted  and  not replaced
entirely.  This can be done in the following way for example  to  intercept
the NMI interrupt routine.

    Initialisation code.

        LDX     BTA_NMI         ; CURRENT SERVICE ROUTINE ADDRESS
        STX     OLD_NMI         ; SAVE THE ADDRESS SOMEWHERE
        LDX     #NEW_NMI        ; NEW NMI ROUTINE ADDRESS
        STX     BTA_NMI         ; RE-DIRECT THE OPERATING SYSTEM

    New NMI routine.

    NEW_NMI:
        ; PERFORM NEW NMI USER CODE
        LDX     OLD_NMI         ; OLD NMI ROUTINE ADDRESS
        JMP     0,X             ; RUN THE OLD ROUTINE



       ________________
5.6.1  HARDWARE VECTORS

     The following is a list of hardware interrupts and  their  vectors  in
RAM.   Those  preceded  by  a  * are not used by the operating system.  The
addresses for the vectors are given in  the  chapter  on  memory  usage  in
section 6.5.1.2.

     1.  *IRQ2 - BTA_2IQ  - Interrupt request 2.

     2.  *CMI  - BTA_CMI  - Timer 2 counter match interrupt.

     3.   TRAP - BTA_TRP  - Trap exception interrupt.

     4.  *SIO  - BTA_SIO  - Serial input/output interrupt.

     5.  *TOI  - BTA_TOI  - Timer 1 overflow interrupt.

     6.   OCI  - BTA_OCI  - Timer output compare interrupt.

     7.  *ICI  - BTA_ICI  - Timer 1 input capture interrupt.

     8.  *IRQ1 - BTA_1IQ  - Interrupt request 1 interrupt.

     9.   SWI  - BTA_SWI  - Software interrupt.

    10.   NMI  - BTA_NMI  - Non-maskable interrupt.




       ________________
5.6.2  SOFTWARE VECTORS

The addresses for the vectors are given in the chapter on memory  usage  in
section 6.5.1.2.

     1.  WARM - BTA_WRM  - Warm start vector.

     2.  SWOF - BTA_SOF  - Power down vector (switch off).

     3.  POLL - BTA_POLL - Keyboard poll routine vector.

     4.  TRAN - BTA_TRAN - Key translate routine vector.




     _____________
5.7  RELEASE NOTES



What follows are notes for the different releases of CM  and  XP  machines.
All significant enhancements and known bugs are listed.

All the bugs noted are fixed for the following release.



       _______________________
5.7.1  VERSION 2.3 AND EARLIER


Not released in any quantity.  Any  machines  with  this  operating  system
should be returned to Psion for update.



       ___________
5.7.2  RELEASE 2.4



Released on 12th May 1986.

ENHANCEMENTS:

     1.  Devices booted when the Organiser is cold booted.

BUGS:

     1.  If the install code of a device alters the menu a crash may  ensue
         on a cold boot.

     2.  Re-booting a machine with more than one device installed may cause
         a crash.

     3.  An attempt to translate the illegal statement "11SIN" results in a
         crash.

     4.  If a field is assigned to that is beyond those already assigned to
         before  it  may  write the data over the diary or operating system
         variables.  This can, in rare cases, result in a crash.   The  fix
         is  to  assign  (a  null  string  or zero) to the last field after
         creating or opening a file and  after  getting  an  END  OF  FILE
         condition.   (The  END  OF FILE condition is when EOF is non-zero,
         this means that all values of the fields have been zeroed out.)

     5.  If the diary is backed over midnight  and  then  brought  forward,
         using the arrow keys, any diary entries seem to have disappeared.

     6.  If RAM is full, editing a procedure can give  OUT  OF  MEMORY  and
         leave the screen corrupted.

     7.  If an error is encountered when adding to or  subtracting  from  a
         calculator memory (M0 to M9) then that memory is corrupted.

     8.  Floating point AND produces unreliable results.

     9.  VIEW(1,"") does not work properly.

    10.  VIEW of a 255 character string doesn't scroll.

    11.  Strings longer than 255 can be  declared  (e.g.  256  gives  a  zero
         length string).

    12.  Declaring arrays which overflow memory size can cause  machine  to
         crash at run-time.  e.g. LOCAL s$(255,100) or LOCAL a(10000).

    13.  INPUT A.A$ artificially limits the length input to 252  minus  the
         record  size  (as  found  from  RECSIZE).   It  should  allow  254
         characters.

    14.  If the machine is turned off in the minute before an alarm is  due
         it won't go off for 34 minutes.

    15.  If packs are accessed at the same time as the buzzer is used  (e.g.
         from a key click) the bottom byte of the pack can, very rarely, be
         blown to zero.




       ___________
5.7.3  RELEASE 2.6



Released on 15 October 1986.

ENHANCEMENTS:

     1.  Checksum on RAM pack header.

     2.  Battery checking improved.

     3.  Can call OPL programs on device D.

     4.  INFO calculates FREE memory as percentage free of the total memory
         less the operating system.

     5.  OPL string comparison become case dependant.

     6.  UDGs preserved when the Organiser is turned off.

     7.  Intelligent, faster NEXT - works on one pack at a time.

     8.  A POSITION to an illegal place, e.g. past the end of file,  used  to
         leave  the  position  alone.   It  now it positions to the last or
         first record as appropriate.

BUGS:

     1.  If after a successful CLOSE another CLOSE is done  when  no  files
         are open it can crash the system.

     2.  It is possible but unlikely to get spurious  alarms  when  loading
         devices.

     3.  If the ON/CLEAR is pressed at the same moment as an alarm  it  may
         be missed.

     4.  When a translator error is detected some memory may be lost  until
         the language is run.

     5.  Using MENU with an item  with  more  than  17  letters  causes  an
         infinite loop.

     6.  When on a null diary entry deleting it causes the next diary entry
         to be deleted.

     7.  TRAP DELETE "A:"+XXX$:  can cause a crash if there is an error  in
         XXX$:.

     8.  If logical name D is used then it can  cause  OPEN  to  fail  with
         error number zero when it should have succeeded.  An error of zero
         is not reported as an error at the top level.  It  is  safest  not
         use logical name D.

     9.  POS200 ONLY.  The menu cell is grown every  time  the  machine  is
         booted  so  memory  eventually fills up.  Solution is to cold boot
         the machine.

INTRODUCED BUGS:

     1.  Sizing 8, 16 & 32K packs can fail even when the pack is good.

     2.  Erasing records on RAMPAKS followed  by  APPEND  may  corrupt  the
         PACK.   Can  be  solved  by  avoiding using UPDATE and doing FIRST
         after using ERASE.

     3.  Copying MK1 packs fails with PACK CHANGED error.




       _______ ___
5.7.4  RELEASE 3.1



Released on 30 January 1987

ENHANCEMENTS:

     1.  If a file is OPENned/CREATEd/DELETEd without a specified device it
         takes the last device used (as opposed to a random device).

     2.  Reports CHR$(256) and negative arguments to LEFT$, RIGHT$ and MID$
         as errors.

     3.  Intelligent NEXT improved  works with 1 file on each device.

     4.  LA split device loader.

     5.  128K RAM packs supported.

     6.  Faster deleting on RAM packs.




     _______________
5.8  SYSTEM SERVICES

       _______
5.8.1  BT$NMDN

VECTOR NUMBER:          007
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service routine switches off NMIs to the processor.

     NOTE:  As the NMI interrupt is used to provide the  system  clock  the
system  time  will be invalid.  It is possible to switch off NMIs and still
maintain a valid system time.  See the system service BT$NOF.

     If NMIs are switched  off  with  this  service  then  they  should  be
switched back on with the BT$NMEN service.

ERRORS:                 None


       _______
5.8.2  BT$NMEN

VECTOR NUMBER:          008
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service routine switches on NMIs to the processor.

     BT$NMEN should only be used to re-establish NMIs  if  they  have  been
disabled with the BT$NMDN service.

ERRORS:                 None



       ______
5.8.3  BT$NOF

VECTOR NUMBER:          009
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service routine switches off NMIs to the processor in such
a way that the system time will be preserved.

     The NMI interrupt is generated from the semi-custom chip every  second
to  provide  a  very accurate system clock.  When NMIs are switched off the
processor, an internal counter in the semi-custom chip is connected to  the
NMI  line so that NMIs can still be counted.  This service ensures that the
counter in the semi-custom chip is reset properly so that on switching NMIs
back  to  the  processor  the time can be updated properly.  In order to do
this it is imperative that the BT$NON service is used to  switch  on  NMIs.
The  maximum  time  that  can  be stored in the counter is 2048 seconds, so
BT$NON must be called before this time has elapsed.

     There is a disadvantage to this pair of services, in that on restoring
NMIs to the processor the BT$NON service must wait for the first NMI before
counting the number of NMIs that have occurred  while  NMIs  were  switched
off.   This means that depending on when in the cycle the BT$NON service is
called a delay of between 0 and 1 second can occur.   See  chapter  10  for
more information on the timing services.

     Finally note that the  counter  used  to  count  NMIs  when  they  are
disabled  from  the processor is also used to scan the keyboard and as such
any keyboard interrupt occurring after BT$NOF has been called will  destroy
the  NMI  counter.   Thus  to  disable  NMIs  and preserve the system time,
interrupts  should  also  be  disabled  before  calling  BT$NOF.   Keyboard
services  must  not be called, as they will poll the keyboard directly when
interrupts are disabled.


     EXAMPLE
        TPA                     ; GET CURRENT STATUS
        PSH     A               ; SAVE IT
        SEI                     ; DISABLE INTERRUPTS
        OS      BT$NOF          ; SWITCH NMIS OFF.
        ; CODE PERFORMED WITH NO INTERRUPTS OCCURRING.
        OS      BT$NON          ; SWITCH NMIS BACK ON AND UPDATE TIME.
        PUL     A               ; RESTORE PREVIOUS STATUS
        TAP                     ; SET STATUS REGISTER

ERRORS:                 None


       ______
5.8.4  BT$NON

VECTOR NUMBER:          010
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service routine switches on NMIs to the processor.

     BT$NON should only be used to re-establish  NMIs  if  they  have  been
disabled with the BT$NOF service.

ERRORS:                 None


       _______
5.8.5  BT$PPRG

VECTOR NUMBER:          011
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service routine will  push  or  pop  the  seven  variables
UTW_R0 to UTW_R6 on the machine stack.

     This system service must be followed by a control byte which  contains
the  instructions  for  the service.  Execution of code continues after the
control byte.

     The format of the control byte is as follows

    BIT 7 - If set then pop the variables else push the variables.
    BIT 6 - If set then push or pop UTW_R6
    BIT 5 - If set then push or pop UTW_R5
    BIT 4 - If set then push or pop UTW_R4
    BIT 3 - If set then push or pop UTW_R3
    BIT 2 - If set then push or pop UTW_R2
    BIT 1 - If set then push or pop UTW_R1
    BIT 0 - If set then push or pop UTW_R0

Thus if the byte value is $5 then UTW_R2 and UTW_R0 will be pushed.

     When pushing, the higher addressed variables are pushed first and when
popping,  the lower address variables are popped first.  Thus if UTW_R5 and
UTW_R2 are pushed and UTW_R2 and UTW_R1 are popped then UTW_R1 will get the
old value of UTW_R2 and UTW_R2 will get the old value of UTW_R5.

     NOTE:  no check is made to ensure that there is room  on  the  machine
stack to take all the variables pushed.

EXAMPLE

        OS      BT$PPRG                 ; PUSH UTW_R0
        .BYTE   1                       ; INSTRUCTION BYTE TO BT$PPRG
        ; CAN NOW USE UTW_R0
        OS      BT$PPRG                 ; POP UTW_R0
        .BYTE   $81                     ; INSTRUCTION BYTE TO BT$PPRG

ERRORS:                 None



       _______
5.8.6  BT$SWOF

VECTOR NUMBER:          012
INPUT PARAMETERS:       None
OUTPUT VALUES:          None

DESCRIPTION


     This system service may be called to switch off the Organiser II.

     When switching off, the service saves the entire state of the  machine
so  that  on  power  up everything is restored to exactly the same state as
when the service was called.  See the section 5.4 for an exact  description
of the power down procedure.

     NOTE that on power up the top 8 bytes of zero page ram (i.e.  $F9-$FF)
are always trashed by the operating system.

     It is easier to intercept the warm startup  routine  via  the  BTA_WRM
vector  to  determine  if the machine has been switched off than to try and
intercept the switch off service via the SWI vector.

EXAMPLE

        OS      BT$SWOF         ; SWITCH OFF THE MACHINE
HERE:                           ; RESTARTS HERE ON POWER UP

ERRORS:                 None