D8B8	ADC &D6     ;add A/&DA to &D6/7
D8BA	STA &D6     ;
D8BC	LDA &DA     ;
D8BE	ADC &D7     ;
D8C0	BPL &D8C6   ;if result +ve D8C6
D8C2	SEC         ;else set carry
D8C3	SBC &0354   ;and subtract screen memory size making it wrap round

D8C6	STA &D7     ;store it in &D7
D8C8	LDY &031A   ;get line in graphics cell containing current graphics
D8CB	LDA #&00    ;point  A=0
D8CD	RTS         ;And exit
   		    ;
D8CE	PHA         ;Push A
D8CF	LDA #&A0    ;A=&A0
D8D1	LDX &026A   ;X=number of items in VDU queque
D8D4	BNE &D916   ;if not 0 D916
D8D6	BIT &D0     ;else check VDU status byte
D8D8	BNE &D916   ;if either VDU is disabled or plot to graphics
   		    ;cursor enabled then D916
D8DA	BVS &D8F5   ;if cursor editing enabled D8F5
D8DC	LDA &035F   ;else get 6845 register start setting
D8DF	AND #&9F    ;clear bits 5 and 6
D8E1	ORA #&40    ;set bit 6 to modify last cursor size setting
D8E3	JSR &C954   ;change write cursor format
D8E6	LDX #&18    ;X=&18
D8E8	LDY #&64    ;Y=&64
D8EA	JSR &D482   ;set text input cursor from text output cursor
D8ED	JSR &CD7A   ;modify character at cursor poistion
D8F0	LDA #&02    ;A=2
D8F2	JSR &C59D   ;bit 1 of VDU status is set to bar scrolling


D8F5	LDA #&BF    ;A=&BF
D8F7	JSR &C5A8   ;bit 6 of VDU status =0
D8FA	PLA         ;Pull A
D8FB	AND #&7F    ;clear hi bit (7)
D8FD	JSR &C4C0   ;entire VDU routine !!
D900	LDA #&40    ;A=&40
D902	JMP &C59D   ;exit


D905	LDA #&20    ;A=&20
D907	BIT &D0     ;if bit 6 cursor editing is set
D909	BVC &D8CB   ;
D90B	BNE &D8CB   ;or bit 5 is set exit &D8CB
D90D	JSR &D7C2   ;read a character from the screen
D910	BEQ &D917   ;if A=0 on return exit via D917
D912	PHA         ;else store A
D913	JSR &C664   ;perform cursor right

D916	PLA         ;restore A
D917	RTS         ;and exit
   		    ;
D918	LDA #&BD    ;zero bits 2 and 6 of VDU status
D91A	JSR &C5A8   ;
D91D	JSR &C951   ;set normal cursor
D920	LDA #&0D    ;A=&0D
D922	RTS         ;and return
   		    ;this is response of CR as end of edit line


*************************************************************************
*                                                                       *
*       OSBYTE 132 - READ BOTTOM OF DISPLAY RAM                         *
*                                                                       *
*************************************************************************
   		    ;
D923	LDX &0355   ;get current screen mode


*************************************************************************
*                                                                       *
*       OSBYTE 133 - READ LOWEST ADDRESS FOR GIVEN MODE                 *
*                                                                       *
*************************************************************************

D926	TXA         ;A=X
D927	AND #&07    ;MOD 8
D929	TAY         ;Y=A
D92A	LDX &C440,Y ;X=get RAM size key
D92D	LDA &C45E,X ;A=high byte of start address
D930	LDX #&00    ;X=0
D932	BIT &028E   ;get available RAM
D935	BMI &D93E   ;if bit 7 set then 32k so D93E
D937	AND #&3F    ;AND A with &3F
D939	CPY #&04    ;if Y<4
D93B	BCS &D93E   ;then D93E
D93D	TXA         ;else A=0 to return null value
D93E	TAY         ;Y=A
D93F	RTS         ;and return


   	
*************************************************************************
*                                                                       *
*       DEFAULT VECTOR TABLE                                            *
*                                                                       *
*************************************************************************

D940	DB  10,E3   ;&E310 = USERV                                  &200
D942	DB  54,DC   ;&DC54 = BRKV                                   &202
D944	DB  93,DC   ;&DC93 = IRQ1V                                  &204
D946	DB  89,DE   ;&DE89 = IRQ2V                                  &206
D948	DB  89,DF   ;&DF89 = CLIV                                   &208
D94A	DB  72,E7   ;&E772 = BYTEV                                  &20A
D94C	DB  EB,E7   ;&E7EB = WORDV                                  &20C
D94E	DB  A4,E0   ;&E0A4 = WRCHV                                  &20E
D950	DB  C5,DE   ;&DEC5 = RDCHV                                  &210
D952	DB  7D,F2   ;&F27D = FILEV                                  &212
D954	DB  8E,F1   ;&F18E = ARGSV                                  &214
D956	DB  C9,F4   ;&F4C9 = BGETV                                  &216
D958	DB  29,F5   ;&F529 = BPUTV                                  &218
D95A	DB  A6,FF   ;&FFA6 = GBPBV                                  &21A
D95C	DB  CA,F3   ;&F3CA = FINDV                                  &21C
D95E	DB  B1,F1   ;&F1B1 = FSCV                                   &21E
D960	DB  A6,FF   ;&FFA6 = EVNTV                                  &220
D962	DB  A6,FF   ;&FFA6 = UPTV                                   &222
D964	DB  A6,FF   ;&FFA6 = NETV                                   &224
D966	DB  A6,FF   ;&FFA6 = VDUV                                   &226
D968	DB  02,EF   ;&EF02 = KEYV                                   &228
D96A	DB  B3,E4   ;&E4B3 = INSBV                                  &22A
D96C	DB  64,E4   ;&E464 = REMVB                                  &22C
D96E	DB  D1,E1   ;&E1D1 = CNPV                                   &22E
D970	DB  A6,FF   ;&FFA6 = IND1V                                  &230
D972	DB  A6,FF   ;&FFA6 = IND2V                                  &232
D974	DB  A6,FF   ;&FFA6 = IND3V                                  &234


*************************************************************************
*                                                                       *
*       MOS VARIABLES DEFAULT SETTINGS                                  *
*                                                                       *
*************************************************************************

*read/written by Osbytes &A6 to &FC
*addresses &236 to &28C = address -&D740

D976	DB  90,01   ;Mos variables address  (address to Add to osbyte
   		    ;number) in lo hi format (&190)                 &236

D978	DB  9F,0D   ;Rom pointer address for indirecting into ROMS
   		    ;=09DF (lo hi format)                           &238

D97A	DB  A1,02   ;ROM information table address (&2A1)           &23A

D97C	DB  2B,F0   ;Key translation table address (&F02B)          &23C

D97E	DB  00,03   ;VDU variables start 0300                       &23E

D980	DB  00      ;CFS/Vertical sync Timeout counter              &240
D981	DB  00      ;current input buffer number                    &241
D982	DB  FF      ;keyboard interrupt processing flag             &242
D983	DB  00      ;primary OSHWM  (default page)                  &243
D984	DB  00      ;current OSHWM  (PAGE)                          &244
D985	DB  01      ;RS423 Mode                                     &245
D986	DB  00      ;character defininition explosion switch        &246
D987	DB  00      ;Filing system flag ROM=2 CFS=0                 &247
D988	DB  00      ;current Video ULA control register             &248
D989	DB  00      ;current pallette setting                       &249
D98A	DB  00      ;number of ROM enabled at last BRK              &24A
D98B	DB  FF      ;number of BASIC ROM                            &24B
D98C	DB  04      ;current ADC channel number                     &24C
D98D	DB  04      ;maximum ADC channel number                     &24D
D98E	DB  00      ;ADC conversion type 0 or 0C=12 bit 8=8 Bit     &24E
D98F	DB  FF      ;RS423 busy flag (bit 7 = 0 =busy)              &24F


D990	DB  56      ;current ACIA control register setting          &250
D991	DB  19      ;flash counter                                  &251
D992	DB  19      ;mark period count                              &252
D993	DB  19      ;space period count                             &253
D994	DB  32      ;keyboard Auto-repeat delay                     &254
D995	DB  08      ;keyboard Auto-repeat rate                      &255
D996	DB  00      ;*EXEC file handle  (0 = not open)              &256
D997	DB  00      ;*SPOOL file handle (0 = not open)              &257
D998	DB  00      ;bit 0 Escape enable/disable                    &258
   		    ;bit 1 BREAK normal/clear memory
D999	DB  00      ;Econet disable keyboard flag                   &259
D99A	DB  20      ;keyboard status        bit 3=1 shift pressed   &25A
   		                            bit 4=0 caps  lock
   		                            bit 5=0 shift lock
   		                            bit 6=1 control bit
   		                            bit 7=1 shift enabled
D99B	DB  09      ;buffer space left at buffer full signal        &25B
D99C	DB  00      ;RS423 input suppression flag                   &25C
D99D	DB  00      ;cassette/RS423 flag  (0=CFS, &40=RS423)        &25D
D99E	DB  00      ;Econet OS call interception flag (bit 7)       &25E
D99F	DB  00      ;Econet OSRDCH interception flag (bit 7)        &25F

D9A0	DB  00      ;Econet OSWRCH interception flag (bit 7)        &260
D9A1	DB  50      ;speech enable/disable flac (50/20)             &261
D9A2	DB  00      ;sound output enable flag                       &262
D9A3	DB  03      ;BELL channel number                            &263
D9A4	DB  90      ;BELL amplitude/Envelope number                 &264
D9A5	DB  64      ;BELL frequency                                 &265
D9A6	DB  06      ;BELL duration                                  &266
D9A7	DB  81      ;bit 7=1 ignore start up message                &267
   		    ;bit 0=1 ignore RFS !BOOT error

D9A8	DB  00      ;length of KEY string                           &268
D9A9	DB  00      ;PRINT line counter                             &269
D9AA	DB  00      ;number of items in VDU queque (2s complement   &26A
   		    ;of number required)
D9AB	DB  09      ;TAB key value                                  &26B
D9AC	DB  1B      ;ESCAPE Character                               &26C

   	;The following are input buffer code interpretation bytes for
   	;keys returning the following keys C0-FF are available via
   	;keypads only!
   	;0=ignore key
   	;1=expand as normal key
   	;2-FF add to base for ASCII code

D9AD	DB  01      ;C0-CF                                          &26D
D9AE	DB  D0      ;D0-DF                                          &26E
D9AF	DB  E0      ;E0-EF                                          &26F
D9B0	DB  F0      ;F0-FF                                          &270
D9B1	DB  01      ;80-8F                                          &271
D9B2	DB  80      ;90-9F                                          &272
D9B3	DB  90      ;A0-AF                                          &273
D9B4	DB  00      ;B0-BF                                          &274


D9B5	DB  00      ;ESCAPE key status (0=ESC, 1,=ASCII)            &275
D9B6	DB  00      ;ESCAPE action                                  &276
D9B7	DB  FF      ;USER 6522 Bit IRQ mask                         &277
D9B8	DB  FF      ;6850 ACIA Bit IRQ bit mask                     &278
D9B9	DB  FF      ;System 6522 IRQ bit mask                       &279
D9BA	DB  00      ;Tube prescence flag                            &27A
D9BB	DB  00      ;speech processor prescence flag                &27B
D9BC	DB  00      ;character destination status                   &27C
D9BD	DB  00      ;cursor editing status                          &27D
   	
****************** Warm reset high water mark ***************************
   	
D9BE	DB  00      ;unused                                         &27E
D9BF	DB  00      ;unused                                         &27F
D9C0	DB  00      ;country code                                   &280
D9C1	DB  00      ;user flag                                      &281
D9C2	DB  64      ;serial ULA control register setting            &282
D9C3	DB  05      ;current system clock store pointer             &283
D9C4	DB  FF      ;soft key status (unstable)                     &284
D9C5	DB  01      ;printer destination                            &285
D9C6	DB  0A      ;printer ignore character                       &286
   	
********* COLD RESET High water mark **************************************
   	
D9C7	DB  00      ;user BREAK routine address JMP                 &288
D9C8	DB  00      ;user BREAK routine address lo                  &288
D9C9	DB  00      ;user BREAK routine address hi                  &289
D9CA	DB  00      ;unused                                         &28A
D9CB	DB  00      ;unused                                         &28B
D9CC	DB  FF      ;current language rom no.                       &28C
   	
*********** POWER-UP RESET High Water mark ********************************
;later flags dealt with in routines





**************************************************************************
**************************************************************************
**                                                                      **
**                                                                      **
**      RESET (BREAK) ENTRY POINT                                       **
**                                                                      **
**      Power up Enter with nothing set, 6522 System VIA IER bits       **
**      0 to 6 will be clear                                            **
**                                                                      **
**      BREAK IER bits 0 to 6 one or more will be set 6522 IER          **
**      not reset by BREAK                                              **
**                                                                      **
**************************************************************************
**************************************************************************

D9CD	LDA #&40    ;set NMI first instruction to RTI
D9CF	STA &0D00   ;NMI ram start

D9D2	SEI         ;disable interrupts just in case
D9D3	CLD         ;clear decimal flag
D9D4	LDX #&FF    ;reset stack to where it should be
D9D6	TXS         ;(&1FF)
D9D7	LDA &FE4E   ;read interupt enable register of the system VIA
D9DA	ASL         ;shift bit 7 into carry
D9DB	PHA         ;save what's left
D9DC	BEQ &D9E7   ;if Power up A=0 so D9E7
D9DE	LDA &0258   ;else if BREAK pressed read BREAK Action flags (set by
   		    ;*FX200,n)
D9E1	LSR         ;divide by 2
D9E2	CMP #&01    ;if (bit 1 not set by *FX200)
D9E4	BNE &DA03   ;then &DA03
D9E6	LSR         ;divide A by 2 again (A=0 if *FX200,2/3 else A=n/4



********** clear store routine ******************************************

D9E7	LDX #&04    ;get page to start clearance from (4)
D9E9	STX &01     ;store it in ZP 01
D9EB	STA &00     ;store A at 00

D9ED	TAY         ;and in Y to set loop counter
   	
D9EE	STA (&00),Y ;clear store
D9F0	CMP &01     ;until address &01 =0
D9F2	BEQ &D9FD   ;
D9F4	INY         ;increment pointer
D9F5	BNE &D9EE   ;if not zero loop round again
D9F7	INY         ;else increment again (Y=1) this avoids overwriting
   		    ;RTI instruction at &D00
D9F8	INX         ;increment X
D9F9	INC &01     ;increment &01
D9FB	BPL &D9EE   ;loop until A=&80 then exit
   		    ;note that RAM addressing for 16k loops around so
   		    ;&4000=&00 hence checking &01 for 00.  This avoids
   		    ;overwriting zero page on BREAK


D9FD	STX &028E   ;writes marker for available RAM 40 =16k,80=32
DA00	STX &0284   ;write soft key consistency flag

**+********** set up system VIA *****************************************

DA03	LDX #&0F    ;set PORT B to output on bits 0-3 Input 4-7
DA05	STX &FE42   ;



*************************************************************************
*                                                                       *
*        set addressable latch IC 32 for peripherals via PORT B         *
*                                                                       *
*       ;bit 3 set sets addressed latch high adds 8 to VIA address      *
*       ;bit 3 reset sets addressed latch low                           *
*                                                                       *
*       Peripheral              VIA bit 3=0             VIA bit 3=1     *
*                                                                       *
*       Sound chip              Enabled                 Disabled        *
*       speech chip (RS)        Low                     High            *
*       speech chip (WS)        Low                     High            *
*       Keyboard Auto Scan      Disabled                Enabled         *
*       C0 address modifier     Low                     High            *
*       C1 address modifier     Low                     High            *
*       Caps lock  LED          ON                      OFF             *
*       Shift lock LED          ON                      OFF             *
*                                                                       *
*       C0 & C1 are involved with hardware scroll screen address        *
*************************************************************************

   	;X=&F on entry

DA08	DEX         ;loop start
DA09	STX &FE40   ;write latch IC32
DA0C	CPX #&09    ;is it 9
DA0E	BCS &DA08   ;if so go back and do it again
   		    ;X=8 at this point
   		    ;Caps lock On, SHIFT lock undetermined
   		    ;Keyboard Autoscan on
   		    ;sound disabled (may still sound)
DA10	INX         ;X=9
DA11	TXA         ;A=X
DA12	JSR &F02A   ;interrogate keyboard
DA15	CPX #&80    ;for keyboard links 9-2 and CTRL key (1)
DA17	ROR &FC     ;rotate MSB into bit 7 of &FC






DA19	TAX         ;get back value of X for loop
DA1A	DEX         ;decrement it
DA1B	BNE &DA11   ;and if >0 do loop again
   		    ; on exit if Carry set link 3 made
   		    ;link 2 = bit 0 of &FC and so on
   		    ;if CTRL pressed bit 7 of &FC=1
   		    ;X=0
DA1D	STX &028D   ;clear last BREAK flag
DA20	ROL &FC     ;CTRL is now in carry &FC is keyboard links
DA22	JSR &EEEB   ;set LEDs carry on entry  bit 7 of A on exit
DA25	ROR         ;get carry back into carry flag

****** set up page 2 ****************************************************

DA26	LDX #&9C    ;
DA28	LDY #&8D    ;
DA2A	PLA         ;get back A from &D9DB
DA2B	BEQ &DA36   ;if A=0 power up reset so DA36 with X=&9C Y=&8D
DA2D	LDY #&7E    ;else Y=&7E
DA2F	BCC &DA42   ;and if not CTRL-BREAK DA42 WARM RESET
DA31	LDY #&87    ;else Y=&87 COLD RESET
DA33	INC &028D   ;&28D=1

DA36	INC &028D   ;&28D=&28D+1
DA39	LDA &FC     ;get keyboard links set
DA3B	EOR #&FF    ;invert
DA3D	STA &028F   ;and store at &28F
DA40	LDX #&90    ;X=&90



**********: set up page 2 *************************************************

   	;on entry        &28D=0 Warm reset, X=&9C, Y=&7E
   		    ;&28D=1 Power up  , X=&90, Y=&8D
   		    ;&28D=2 Cold reset, X=&9C, Y=&87

DA42	LDA #&00    ;A=0
DA44	CPX #&CE    ;zero &200+X to &2CD
DA46	BCC &DA4A   ;
DA48	LDA #&FF    ;then set &2CE to &2FF to &FF
DA4A	STA &0200,X ;
DA4D	INX         ;
DA4E	BNE &DA44   ;
   		    ;A=&FF X=0
DA50	STA &FE63   ;set port A of user via to all outputs (printer out)