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+*************************************************************************
*                                                                       *
*       VDU 24 - DEFINE GRAPHICS WINDOW                                 *
*                                                                       *
*       8 parameters                                                    *
*                                                                       *
*************************************************************************
;&31C/D Left margin
;&31E/F Bottom margin
;&320/1 Right margin
;&322/3 Top margin

CA39	JSR &CA81   ;exchange 310/3 with 328/3
CA3C	LDX #&1C    ;
CA3E	LDY #&2C    ;
CA40	JSR &D411   ;calculate width=right - left
    	            ;          height = top-bottom
CA43	ORA &032D   ;
CA46	BMI &CA81   ;exchange 310/3 with 328/3 and exit
CA48	LDX #&20    ;X=&20
CA4A	JSR &D149   ;scale pointers to mode
CA4D	LDX #&1C    ;X=&1C
CA4F	JSR &D149   ;scale pointers to mode
CA52	LDA &031F   ;check for negative margins
CA55	ORA &031D   ;
CA58	BMI &CA81   ;if found exchange 310/3 with 328/3 and exit
CA5A	LDA &0323   ;
CA5D	BNE &CA81   ;exchange 310/3 with 328/3 and exit
CA5F	LDX &0355   ;screen mode
CA62	LDA &0321   ;right margin hi
CA65	STA &DA     ;store it
CA67	LDA &0320   ;right margin lo
CA6A	LSR &DA     ;/2
CA6C	ROR         ;A=A/2
CA6D	LSR &DA     ;/2
CA6F	BNE &CA81   ;exchange 310/3 with 328/3
CA71	ROR         ;A=A/2
CA72	LSR         ;A=A/2
CA73	CMP C3EF,X  ;text window right hand margin maximum
CA76	BEQ &CA7A   ;if equal CA7A
CA78	BPL &CA81   ;exchange 310/3 with 328/3

CA7A	LDY #&00    ;Y=0
CA7C	LDX #&1C    ;X=&1C
CA7E	JSR &D47C   ;set(300/7+Y) from (300/7+X)


***************** exchange 310/3 with 328/3 *****************************

CA81	LDX #&10    ;X=10
CA83	LDY #&28    ;Y=&28
CA85	JMP &CDE6   ;exchange 300/3+Y and 300/3+X

CA88	INY         ;Y=Y+1
CA89	TYA         ;A=Y
CA8A	LDY #&00    ;Y=0
CA8C	STY &034D   ;text window width hi (bytes)
CA8F	STA &034C   ;text window width lo (bytes)
CA92	LDA &034F   ;bytes per character
CA95	LSR         ;/2
CA96	BEQ &CAA1   ;if 0 exit
CA98	ASL &034C   ;text window width lo (bytes)
CA9B	ROL &034D   ;text window width hi (bytes)
CA9E	LSR         ;/2
CA9F	BCC &CA98   ;
CAA1	RTS         ;


*************************************************************************
*                                                                       *
*       VDU 29 - SET GRAPHICS ORIGIN                                    *
*                                                                       *
*       4 parameters                                                    *
*                                                                       *
*************************************************************************
;
CAA2	LDX #&20    ;
CAA4	LDY #&0C    ;
CAA6	JSR &D48A   ;(&300/3+Y)=(&300/3+X)
CAA9	JMP &D1B8   ;set up external coordinates for graphics


*************************************************************************
*                                                                       *
*       VDU 127 (&7F) - DELETE (entry 32)                               *
*                                                                       *
*************************************************************************

CAAC	JSR &C5C5   ;cursor left
CAAF	JSR &C588   ;A=0 if text cursor A=&20 if graphics cursor
CAB2	BNE &CAC7   ;if graphics then CAC7
CAB4	LDX &0360   ;number of logical colours less 1
CAB7	BEQ &CAC2   ;if mode 7 CAC2
CAB9	STA &DE     ;else store A (always 0)
CABB	LDA #&C0    ;A=&C0
CABD	STA &DF     ;store in &DF (&DE) now points to C300 SPACE pattern
CABF	JMP &CFBF   ;display a space

CAC2	LDA #&20    ;A=&20
CAC4	JMP &CFDC   ;and return to display a space

CAC7	LDA #&7F    ;for graphics cursor
CAC9	JSR &D03E   ;set up character definition pointers
CACC	LDX &035A   ;Background graphics colour
CACF	LDY #&00    ;Y=0
CAD1	JMP &CF63   ;invert pattern data (to background colour)


***** Add number of bytes in a line to X/A ******************************

CAD4	PHA         ;store A
CAD5	TXA         ;A=X
CAD6	CLC         ;clear carry
CAD7	ADC &0352   ;bytes per character row
CADA	TAX         ;X=A
CADB	PLA         ;get back A
CADC	ADC &0353   ;bytes per character row
CADF	RTS         ;and return
;
********* control scrolling in paged mode *******************************

CAE0	JSR &CB14   ;zero paged mode line counter
CAE3	JSR &E9D9   ;osbyte 118 check keyboard status; set LEDs
CAE6	BCC &CAEA   ;if carry clear CAEA
CAE8	BMI &CAE0   ;if M set CAE0 do it again

CAEA	LDA &D0     ;VDU status byte
CAEC	EOR #&04    ;invert bit 2 paged scrolling
CAEE	AND #&46    ;and if 2 cursors, paged mode off, or scrolling
CAF0	BNE &CB1C   ;barred then CB1C to exit

CAF2	LDA &0269   ;paged mode counter
CAF5	BMI &CB19   ;if negative then exit via CB19



CAF7	LDA &0319   ;current text line
CAFA	CMP &0309   ;bottom margin
CAFD	BCC &CB19   ;increment line counter and exit

CAFF	LSR         ;A=A/4
CB00	LSR         ;
CB01	SEC         ;set carry
CB02	ADC &0269   ;paged mode counter
CB05	ADC &030B   ;top of text window
CB08	CMP &0309   ;bottom margin
CB0B	BCC &CB19   ;increment line counter and exit

CB0D	CLC         ;clear carry
CB0E	JSR &E9D9   ;osbyte 118 check keyboard status; set LEDs
CB11	SEC         ;set carry
CB12	BPL &CB0E   ;if +ve result then loop till shift pressed


**************** zero paged mode  counter *******************************

CB14	LDA #&FF    ;
CB16	STA &0269   ;paged mode counter
CB19	INC &0269   ;paged mode counter
CB1C	RTS         ;
;

*********part of intitialisation routines ******************************

CB1D	PHA         ;save A
CB1E	LDX #&7F    ;X=&7F
CB20	LDA #&00    ;A=0
CB22	STA &D0     ;VDU status byte to set default conditions

CB24	STA &02FF,X ;zero 300,37E
CB27	DEX         ;with this loop
CB28	BNE &CB24   ;

CB2A	JSR &CD07   ;implode character definitions
CB2D	PLA         ;get back A
CB2E	LDX #&7F    ;X=&7F
CB30	STX &0366   ;mode 7 write cursor character
CB33	BIT &028E   ;available RAM pages
CB36	BMI &CB3A   ;if 32k CB3A

CB38	ORA #&04    ;ensure only modes 4-7 are available

CB3A	AND #&07    ;X=A and 7 ensure legal mode
CB3C	TAX         ;X=mode
CB3D	STX &0355   ;set screen mode flag
CB40	LDA &C414,X ;no. of colours -1 in mode table
CB43	STA &0360   ;number of logical colours less 1
CB46	LDA &C3FF,X ;number of bytes /character for each mode
CB49	STA &034F   ;bytes per character
CB4C	LDA &C43A,X ;display mode pixels/byte table
CB4F	STA &0361   ;pixels per byte
CB52	BNE &CB56   ;if <> 0 CB56
CB54	LDA #&07    ;else A=7

CB56	ASL         ;A=A*2
CB57	TAY         ;Y=A






CB58	LDA &C406,Y ;mask table
CB5B	STA &0363   ;colour mask left
CB5E	ASL         ;A=A*2
CB5F	BPL &CB5E   ;If still +ve CB5E
CB61	STA &0362   ;colour mask right
CB64	LDY &C440,X ;screen display memory index table
CB67	STY &0356   ;memory map type
CB6A	LDA &C44F,Y ;VDU section control
CB6D	JSR &E9F8   ;set hardware scrolling to VIA
CB70	LDA &C44B,Y ;VDU section control
CB73	JSR &E9F8   ;set hardware scrolling to VIA
CB76	LDA &C459,Y ;Screen RAM size hi byte table
CB79	STA &0354   ;screen RAM size hi byte
CB7C	LDA &C45E,Y ;screen ram address hi byte
CB7F	STA &034E   ;hi byte of screen RAM address
CB82	TYA         ;Y=A
CB83	ADC #&02    ;Add 2
CB85	EOR #&07    ;
CB87	LSR         ;/2
CB88	TAX         ;X=A
CB89	LDA &C466,X ;row multiplication table pointer
CB8C	STA &E0     ;store it
CB8E	LDA #&C3    ;A=&C3
CB90	STA &E1     ;store it (&E0) now points to C3B5 or C375
CB92	LDA &C463,X ;get nuber of bytes per row from table
CB95	STA &0352   ;store as bytes per character row
CB98	STX &0353   ;bytes per character row
CB9B	LDA #&43    ;A=&43
CB9D	JSR &C5A8   ;A=A and &D0:&D0=A
CBA0	LDX &0355   ;screen mode
CBA3	LDA &C3F7,X ;get video ULA control setting
CBA6	JSR &EA00   ;set video ULA using osbyte 154
CBA9	PHP         ;push flags
CBAA	SEI         ;set interrupts
CBAB	LDX &C469,Y ;get cursor end register data from table
CBAE	LDY #&0B    ;Y=11

CBB0	LDA &C46E,X ;get end of 6845 registers 0-11 table
CBB3	JSR &C95E   ;set register Y
CBB6	DEX         ;reduce pointers
CBB7	DEY         ;
CBB8	BPL &CBB0   ;and if still >0 do it again

CBBA	PLP         ;pull flags
CBBB	JSR &C839   ;set default colours
CBBE	JSR &C9BD   ;set default windows

CBC1	LDX #&00    ;X=0
CBC3	LDA &034E   ;hi byte of screen RAM address
CBC6	STX &0350   ;window area start address lo
CBC9	STA &0351   ;window area start address hi
CBCC	JSR &C9F6   ;use X and Y to set new cursor address
CBCF	LDY #&0C    ;Y=12
CBD1	JSR &CA2B   ;set registers 12 and 13 in CRTC
CBD4	LDA &0358   ;background text colour
CBD7	LDX &0356   ;memory map type
CBDA	LDY &C454,X ;get section control number
CBDD	STY &035D   ;set it in jump vector lo
CBE0	LDY #&CC    ;Y=&CC
CBE2	STY &035E   ;upper byte of link address
CBE5	LDX #&00    ;X=0
CBE7	STX &0269   ;paged mode counter
CBEA	STX &0318   ;text column
CBED	STX &0319   ;current text line
CBF0	JMP (&035D) ;jump vector set up previously


*************************************************************************
*                                                                       *
*       OSWORD 10 - READ CHARACTER DEFINITION                           *
*                                                                       *
*************************************************************************
;&EF=A:&F0=X:&F1=Y, on entry YX contains number of byte to be read
;(&DE) points to address
;on exit byte YX+1 to YX+8 contain definition

CBF3	JSR &D03E   ;set up character definition pointers
CBF6	LDY #&00    ;Y=0
CBF8	LDA (&DE),Y ;get first byte
CBFA	INY         ;Y=Y+1
CBFB	STA (&F0),Y ;store it in YX
CBFD	CPY #&08    ;until Y=8
CBFF	BNE &CBF8   ;
CC01	RTS         ;then exit
;

*************************************************************************
*                                                                       *
*       MAIN SCREEN CLEARANCE ROUTINE                                   *
*                                                                       *
*************************************************************************
;on entry A contains background colour which is set in every byte
;of the screen

************************ Mode 0,1,2 entry point *************************

CC02	STA &3000,X ;
CC05	STA &3100,X ;
CC08	STA &3200,X ;
CC0B	STA &3300,X ;
CC0E	STA &3400,X ;
CC11	STA &3500,X ;
CC14	STA &3600,X ;
CC17	STA &3700,X ;
CC1A	STA &3800,X ;
CC1D	STA &3900,X ;
CC20	STA &3A00,X ;
CC23	STA &3B00,X ;
CC26	STA &3C00,X ;
CC29	STA &3D00,X ;
CC2C	STA &3E00,X ;
CC2F	STA &3F00,X ;

************************ Mode 3 entry point *****************************

CC32	STA &4000,X ;
CC35	STA &4100,X ;
CC38	STA &4200,X ;
CC3B	STA &4300,X ;
CC3E	STA &4400,X ;
CC41	STA &4500,X ;
CC44	STA &4600,X ;
CC47	STA &4700,X ;
CC4A	STA &4800,X ;
CC4D	STA &4900,X ;
CC50	STA &4A00,X ;
CC53	STA &4B00,X ;
CC56	STA &4C00,X ;
CC59	STA &4D00,X ;
CC5C	STA &4E00,X ;
CC5F	STA &4F00,X ;
CC62	STA &5000,X ;
CC65	STA &5100,X ;
CC68	STA &5200,X ;
CC6B	STA &5300,X ;
CC6E	STA &5400,X ;
CC71	STA &5500,X ;
CC74	STA &5600,X ;
CC77	STA &5700,X ;

************************ Mode 4,5 entry point ***************************

CC7A	STA &5800,X ;
CC7D	STA &5900,X ;
CC80	STA &5A00,X ;
CC83	STA &5B00,X ;
CC86	STA &5C00,X ;
CC89	STA &5D00,X ;
CC8C	STA &5E00,X ;
CC8F	STA &5F00,X ;

************************ Mode 6 entry point *****************************

CC92	STA &6000,X ;
CC95	STA &6100,X ;
CC98	STA &6200,X ;
CC9B	STA &6300,X ;
CC9E	STA &6400,X ;
CCA1	STA &6500,X ;
CCA4	STA &6600,X ;
CCA7	STA &6700,X ;
CCAA	STA &6800,X ;
CCAD	STA &6900,X ;
CCB0	STA &6A00,X ;
CCB3	STA &6B00,X ;
CCB6	STA &6C00,X ;
CCB9	STA &6D00,X ;
CCBC	STA &6E00,X ;
CCBF	STA &6F00,X ;
CCC2	STA &7000,X ;
CCC5	STA &7100,X ;
CCC8	STA &7200,X ;
CCCB	STA &7300,X ;
CCCE	STA &7400,X ;
CCD1	STA &7500,X ;
CCD4	STA &7600,X ;
CCD7	STA &7700,X ;
CCDA	STA &7800,X ;
CCDD	STA &7900,X ;
CCE0	STA &7A00,X ;
CCE3	STA &7B00,X ;

************************ Mode 7 entry point *****************************

CCE6	STA &7C00,X ;
CCE9	STA &7D00,X ;
CCEC	STA &7E00,X ;
CCEF	STA &7F00,X ;
CCF2	INX         ;
CCF3	BEQ &CD65   ;exit

****************** execute required function ****************************

CCF5	JMP (&035D) ;jump vector set up previously




********* subtract bytes per line from X/A ******************************

CCF8	PHA         ;Push A
CCF9	TXA         ;A=X
CCFA	SEC         ;set carry for subtraction
CCFB	SBC &0352   ;bytes per character row
CCFE	TAX         ;restore X
CCFF	PLA         ;and A
CD00	SBC &0353   ;bytes per character row
CD03	CMP &034E   ;hi byte of screen RAM address
CD06	RTS         ;return


*************************************************************************
*                                                                       *
*       OSBYTE 20 - EXPLODE CHARACTERS                                  *
*                                                                       *
*************************************************************************
;
CD07	LDA #&0F    ;A=15
CD09	STA &0367   ;font flag indicating that page &0C,&C0-&C2 are
    	            ;used for user defined characters
CD0C	LDA #&0C    ;A=&0C
CD0E	LDY #&06    ;set loop counter

CD10	STA &0368,Y ;set all font location bytes
CD13	DEY         ;to page &0C to indicate only page available
CD14	BPL &CD10   ;for user character definitions

CD16	CPX #&07    ;is X= 7 or greater
CD18	BCC &CD1C   ;if not CD1C
CD1A	LDX #&06    ;else X=6
CD1C	STX &0246   ;character definition explosion switch
CD1F	LDA &0243   ;A=primary OSHWM
CD22	LDX #&00    ;X=0

CD24	CPX &0246   ;character definition explosion switch
CD27	BCS &CD34   ;
CD29	LDY &C4BA,X ;get soft character  RAM allocation
CD2C	STA &0368,Y ;font location bytes
CD2F	ADC #&01    ;Add 1
CD31	INX         ;X=X+1
CD32	BNE &CD24   ;if X<>0 then CD24

CD34	STA &0244   ;current value of page (OSHWM)
CD37	TAY         ;Y=A
CD38	BEQ &CD06   ;return via CD06 (ERROR?)

CD3A	LDX #&11    ;X=&11
CD3C	JMP &F168   ;issue paged ROM service call &11
    	            ;font implosion/explosion warning

******** move text cursor to next line **********************************

CD3F	LDA #&02    ;A=2 to check if scrolling disabled
CD41	BIT &D0     ;VDU status byte
CD43	BNE &CD47   ;if scrolling is barred CD47
CD45	BVC &CD79   ;if cursor editing mode disabled RETURN

CD47	LDA &0309   ;bottom margin
CD4A	BCC &CD4F   ;if carry clear on entry CD4F
CD4C	LDA &030B   ;else if carry set get top of text window
CD4F	BVS &CD59   ;and if cursor editing enabled CD59
CD51	STA &0319   ;get current text line
CD54	PLA         ;pull return link from stack
CD55	PLA         ;
CD56	JMP &C6AF   ;set up cursor and display address

CD59	PHP         ;push flags
CD5A	CMP &0365   ;Y coordinate of text input cursor
CD5D	BEQ &CD78   ;if A=line count of text input cursor CD78 to exit
CD5F	PLP         ;get back flags
CD60	BCC &CD66   ;
CD62	DEC &0365   ;Y coordinate of text input cursor

CD65	RTS         ;exit
;
CD66	INC &0365   ;Y coordinate of text input cursor
CD69	RTS         ;exit


*********************** set up write cursor ********************************

CD6A	PHP         ;save flags
CD6B	PHA         ;save A
CD6C	LDY &034F   ;bytes per character
CD6F	DEY         ;Y=Y-1
CD70	BNE &CD8F   ;if Y=0 Mode 7 is in use

CD72	LDA &0338   ;so get mode 7 write character cursor character &7F
CD75	STA (&D8),Y ;store it at top scan line of current character
CD77	PLA         ;pull A
CD78	PLP         ;pull flags
CD79	RTS         ;and exit
;
CD7A	PHP         ;push flags
CD7B	PHA         ;push A
CD7C	LDY &034F   ;bytes per character
CD7F	DEY         ;
CD80	BNE &CD8F   ;if not mode 7
CD82	LDA (&D8),Y ;get cursor from top scan line
CD84	STA &0338   ;store it
CD87	LDA &0366   ;mode 7 write cursor character
CD8A	STA (&D8),Y ;store it at scan line
CD8C	JMP &CD77   ;and exit

CD8F	LDA #&FF    ;A=&FF =cursor
CD91	CPY #&1F    ;except in mode 2 (Y=&1F)
CD93	BNE &CD97   ;if not CD97
CD95	LDA #&3F    ;load cursor byte mask


********** produce white block write cursor *****************************

CD97	STA &DA     ;store it
CD99	LDA (&D8),Y ;get scan line byte
CD9B	EOR &DA     ;invert it
CD9D	STA (&D8),Y ;store it on scan line
CD9F	DEY         ;decrement scan line counter
CDA0	BPL &CD99   ;do it again
CDA2	BMI &CD77   ;then jump to &CD77

CDA4	JSR &CE5B   ;exchange line and column cursors with workspace copies
CDA7	LDA &0309   ;bottom margin
CDAA	STA &0319   ;current text line
CDAD	JSR &CF06   ;set up display address
CDB0	JSR &CCF8   ;subtract bytes per character row from this
CDB3	BCS &CDB8   ;wraparound if necessary
CDB5	ADC &0354   ;screen RAM size hi byte
CDB8	STA &DB     ;store A
CDBA	STX &DA     ;X
CDBC	STA &DC     ;A again
CDBE	BCS &CDC6   ;if C set there was no wraparound so CDC6
CDC0	JSR &CE73   ;copy line to new position
    	            ;using (&DA) for read
    	            ;and (&D8) for write
CDC3	JMP &CDCE   ;

CDC6	JSR &CCF8   ;subtract bytes per character row from X/A
CDC9	BCC &CDC0   ;if a result is outside screen RAM CDC0
CDCB	JSR &CE38   ;perform a copy

CDCE	LDA &DC     ;set write pointer from read pointer
CDD0	LDX &DA     ;
CDD2	STA &D9     ;
CDD4	STX &D8     ;
CDD6	DEC &DE     ;decrement window height
CDD8	BNE &CDB0   ;and if not zero CDB0
CDDA	LDX #&28    ;point to workspace
CDDC	LDY #&18    ;point to text column/line
CDDE	LDA #&02    ;number of bytes to swap
CDE0	BNE &CDE8   ;exchange (328/9)+Y with (318/9)+X
CDE2	LDX #&24    ;point to graphics cursor
CDE4	LDY #&14    ;point to last graphics cursor
    	            ;A=4 to swap X and Y coordinates


*************** exchange 300/3+Y with 300/3+X ***************************

CDE6	LDA #&04    ;A =4


************** exchange (300/300+A)+Y with (300/300+A)+X *****************

CDE8	STA &DA     ;store it as loop counter

CDEA	LDA &0300,X ;get byte
\ No newline at end of file