mirror of
https://github.com/vxunderground/MalwareSourceCode
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271 lines
13 KiB
NASM
271 lines
13 KiB
NASM
INTERRUPTS SEGMENT AT 0H ;This is where the keyboard interrupt
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ORG 9H*4 ;holds the address of its service routine
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KEYBOARD_INT LABEL DWORD
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INTERRUPTS ENDS
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SCREEN SEGMENT AT 0B000H ;A dummy segment to use as the
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SCREEN ENDS ;Extra Segment
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ROM_BIOS_DATA SEGMENT AT 40H ;BIOS statuses held here, also keyboard buffer
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ORG 1AH
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HEAD DW ? ;Unread chars go from Head to Tail
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TAIL DW ?
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BUFFER DW 16 DUP (?) ;The buffer itself
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BUFFER_END LABEL WORD
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ROM_BIOS_DATA ENDS
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CODE_SEG SEGMENT
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ASSUME CS:CODE_SEG
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ORG 100H ;ORG = 100H to make this into a .COM file
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FIRST: JMP LOAD_PAD ;First time through jump to initialize routine
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CNTRL_N_FLAG DW 0 ;Cntrl-N on or off
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PAD DB '_',499 DUP(' ') ;Memory storage for pad
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PAD_CURSOR DW 0 ;Current position in pad
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PAD_OFFSET DW 0 ;Chooses 1st 250 bytes or 2nd
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FIRST_POSITION DW ? ;Position of 1st char on screen
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ATTRIBUTE DB 112 ;Pad Attribute -- reverse video
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SCREEN_SEG_OFFSET DW 0 ;0 for mono, 8000H for graphics
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IO_CHAR DW ? ;Holds addr of Put or Get_Char
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STATUS_PORT DW ? ;Video controller status port
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OLD_KEYBOARD_INT DD ? ;Location of old kbd interrupt
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N_PAD PROC NEAR ;The keyboard interrupt will now come here.
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ASSUME CS:CODE_SEG
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PUSH AX ;Save the used registers for good form
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PUSH BX
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PUSH CX
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PUSH DX
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PUSH DI
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PUSH SI
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PUSH DS
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PUSH ES
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PUSHF ;First, call old keyboard interrupt
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CALL OLD_KEYBOARD_INT
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ASSUME DS:ROM_BIOS_DATA ;Examine the char just put in
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MOV BX,ROM_BIOS_DATA
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MOV DS,BX
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MOV BX,TAIL ;Point to current tail
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CMP BX,HEAD ;If at head, kbd int has deleted char
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JE IN ;So leave
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SUB BX,2 ;Point to just read in character
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CMP BX,OFFSET BUFFER ;Did we undershoot buffer?
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JAE NO_WRAP ;Nope
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MOV BX,OFFSET BUFFER_END ;Yes -- move to buffer top
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SUB BX,2
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NO_WRAP:MOV DX,[BX] ;Char in DX now
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CMP DX,310EH ;Is the char a Cntrl-N?
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JNE NOT_CNTRL_N ;No
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MOV TAIL,BX ;Yes -- delete it from buffer
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NOT CNTRL_N_FLAG ;Switch Modes
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CMP CNTRL_N_FLAG,0 ;Cntrl-N off?
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JNE CNTRL_N_ON ;No, only other choice is on
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CNTRL_N_OFF:
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MOV ATTRIBUTE,7 ;Set up for normal video
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MOV PAD_OFFSET,250 ;Point to 2nd half of pad
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LEA AX,PUT_CHAR ;Make IO call Put_Char as it scans
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MOV IO_CHAR,AX ;over all locations in pad on screen
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CALL IO ;Restore screen
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IN: JMP OUT ;Done
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CNTRL_N_ON:
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MOV PAD_OFFSET,250 ;Point to screen stroage part of pad
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LEA AX,GET_CHAR ;Make IO use Get_char so current screen
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MOV IO_CHAR,AX ;is stored
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CALL IO ;Store Screen
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CALL DISPLAY ;And put up the pad
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JMP OUT ;Done here.
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NOT_CNTRL_N:
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TEST CNTRL_N_FLAG,1 ;Is Cntrl-N on?
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JZ IN ;No -- leave
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MOV TAIL,BX ;Yes, delete this char from buffer
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CMP DX,5300H ;Decide what to do -- is it a Delete?
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JNE RUBOUT_TEST ;No -- try Rubout
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MOV BX,249 ;Yes -- fill pad with spaces
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DEL_LOOP:
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MOV PAD[BX],' ' ;Move space to current pad position
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DEC BX ;and go back one
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JNZ DEL_LOOP ;until done.
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MOV PAD,'_' ;Put the cursor at the beginning
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MOV PAD_CURSOR,0 ;And start cursor over
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CALL DISPLAY ;Put up the new pad on screen
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JMP OUT ;And take our leave
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RUBOUT_TEST:
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CMP DX,0E08H ;Is it a Rubout?
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JNE CRLF_TEST ;No -- try carriage return-line feed
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MOV BX,PAD_CURSOR ;Yes -- get current pad location
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CMP BX,0 ;Are we at beginning?
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JLE NEVER_MIND ;Yes -- can't rubout past beginning
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MOV PAD[BX],' ' ;No -- move space to current position
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MOV PAD[BX-1],'_' ;And move cursor back one
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DEC PAD_CURSOR ;Set the pad location straight
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NEVER_MIND:
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CALL DISPLAY ;And put the result on the screen
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JMP OUT ;Done here.
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CRLF_TEST:
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CMP DX,1C0DH ;Is it a carriage return-line feed?
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JNE CHAR_TEST ;No -- put it in the pad
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CALL CRLF ;Yes -- move to next line
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CALL DISPLAY ;And display result on screen
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JMP OUT ;Done.
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CHAR_TEST:
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MOV BX,PAD_CURSOR ;Get current pad location
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CMP BX,249 ;Are we past the end of the pad?
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JGE PAST_END ;Yes -- throw away char
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MOV PAD[BX],DL ;No -- move ASCII code into pad
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MOV PAD[BX+1],'_' ;Advance cursor
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INC PAD_CURSOR ;Increment pad location
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PAST_END:
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CALL DISPLAY ;Put result on screen
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OUT: POP ES ;Having done Pushes, here are the Pops
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POP DS
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POP SI
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POP DI
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POP DX
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POP CX
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POP BX
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POP AX
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IRET ;An interrupt needs an IRET
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N_PAD ENDP
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DISPLAY PROC NEAR ;Puts the whole pad on the screen
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PUSH AX
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MOV ATTRIBUTE,112 ;Use reverse video
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MOV PAD_OFFSET,0 ;Use 1st 250 bytes of pad memory
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LEA AX,PUT_CHAR ;Make IO use Put-Char so it does
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MOV IO_CHAR,AX
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CALL IO ;Put result on screen
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POP AX
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RET ;Leave
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DISPLAY ENDP
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CRLF PROC NEAR ;This handles carriage returns
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CMP PAD_CURSOR,225 ;Are we on last line?
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JGE DONE ;Yes, can't do a carriage return, exit
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NEXT_CHAR:
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MOV BX,PAD_CURSOR ;Get pad location
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MOV AX,BX ;Get another copy for destructive tests
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EDGE_TEST:
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CMP AX,24 ;Are we at the edge of the pad display?
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JE AT_EDGE ;Yes -- fill pad with new cursor
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JL ADD_SPACE ;No -- Advance another space
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SUB AX,25 ;Subtract another line-width
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JMP EDGE_TEST ;Check if at edge now
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ADD_SPACE:
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MOV PAD[BX],' ' ;Add a space
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INC PAD_CURSOR ;Update pad location
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JMP NEXT_CHAR ;Check if at edge now
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AT_EDGE:
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MOV PAD[BX+1],'_' ;Put cursor in next location
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INC PAD_CURSOR ;Update pad location to new cursor
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DONE: RET ;And out.
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CRLF ENDP
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GET_CHAR PROC NEAR ;Gets a char from screen and advances position
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PUSH DX
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MOV SI,2 ;Loop twice, once for char, once for attribute
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MOV DX,STATUS_PORT ;Get ready to read video controller status
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G_WAIT_LOW: ;Start waiting for a new horizontal scan -
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IN AL,DX ;Make sure the video controller scan status
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TEST AL,1 ;is low
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JNZ G_WAIT_LOW
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G_WAIT_HIGH: ;After port has gone low, it must go high
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IN AL,DX ;before it is safe to read directly from
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TEST AL,1 ;the screen buffer in memory
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JZ G_WAIT_HIGH
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MOV AH,ES:[DI] ;Do the move from the screen, one byte at a time
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INC DI ;Move to next screen location
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DEC SI ;Decrement loop counter
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CMP SI,0 ;Are we done?
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JE LEAVE ;Yes
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MOV PAD[BX],AH ;No -- put char we got into the pad
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JMP G_WAIT_LOW ;Do it again
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LEAVE: INC BX ;Update pad location
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POP DX
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RET
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GET_CHAR ENDP
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PUT_CHAR PROC NEAR ;Puts one char on screen and advances position
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PUSH DX
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MOV AH,PAD[BX] ;Get the char to be put onto the screen
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MOV SI,2 ;Loop twice, once for char, once for attribute
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MOV DX,STATUS_PORT ;Get ready to read video controller status
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P_WAIT_LOW: ;Start waiting for a new horizontal scan -
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IN AL,DX ;Make sure the video controller scan status
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TEST AL,1 ;is low
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JNZ P_WAIT_LOW
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P_WAIT_HIGH: ;After port has gone low, it must go high
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IN AL,DX ;before it is safe to write directly to
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TEST AL,1 ;the screen buffer in memory
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JZ P_WAIT_HIGH
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MOV ES:[DI],AH ;Move to screen, one byte at a time
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MOV AH,ATTRIBUTE ;Load attribute byte for second pass
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INC DI ;Point to next screen postion
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DEC SI ;Decrement loop counter
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JNZ P_WAIT_LOW ;If not zero, do it one more time
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INC BX ;Point to next char in pad
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POP DX
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RET ;Exeunt
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PUT_CHAR ENDP
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IO PROC NEAR ;This scans over all screen positions of the pad
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ASSUME ES:SCREEN ;Use screen as extra segment
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MOV BX,SCREEN
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MOV ES,BX
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MOV DI,SCREEN_SEG_OFFSET ;DI will be pointer to screen postion
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ADD DI,FIRST_POSITION ;Add width of screen minus pad width
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MOV BX,PAD_OFFSET ;BX will be pad location pointer
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MOV CX,10 ;There will be 10 lines
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LINE_LOOP:
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MOV DX,25 ;And 25 spaces across
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CHAR_LOOP:
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CALL IO_CHAR ;Call Put-Char or Get-Char
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DEC DX ;Decrement character loop counter
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JNZ CHAR_LOOP ;If not zero, scan over next character
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ADD DI,FIRST_POSITION ;Add width of screen minus pad width
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LOOP LINE_LOOP ;And now go back to do next line
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RET ;Finished
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IO ENDP
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LOAD_PAD PROC NEAR ;This procedure intializes everything
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ASSUME DS:INTERRUPTS ;The data segment will be the Interrupt area
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MOV AX,INTERRUPTS
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MOV DS,AX
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MOV AX,KEYBOARD_INT ;Get the old interrupt service routine
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MOV OLD_KEYBOARD_INT,AX ;address and put it into our location
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MOV AX,KEYBOARD_INT[2] ;OLD_KEYBOARD_INT so we can call it.
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MOV OLD_KEYBOARD_INT[2],AX
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MOV KEYBOARD_INT,OFFSET N_PAD ;Now load the address of our notepad
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MOV KEYBOARD_INT[2],CS ;routine into the keyboard interrupt
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MOV AH,15 ;Ask for service 15 of INT 10H
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INT 10H ;This tells us how display is set up
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SUB AH,25 ;Move to twenty places before edge
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SHL AH,1 ;Mult by two (char & attribute bytes)
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MOV BYTE PTR FIRST_POSITION,AH ;Set screen cursor
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MOV STATUS_PORT,03BAH ;Assume this is a monochrome display
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TEST AL,4 ;Is it?
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JNZ EXIT ;Yes - jump out
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MOV SCREEN_SEG_OFFSET,8000H ;No - set up for graphics display
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MOV STATUS_PORT,03DAH
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EXIT: MOV DX,OFFSET LOAD_PAD ;Set up everything but LOAD_PAD to
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INT 27H ;stay and attach itself to DOS
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LOAD_PAD ENDP
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CODE_SEG ENDS
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END FIRST ;END "FIRST" so 8088 will go to FIRST first.
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