COMMENT * CLUBware (tm) XREP repeates an input character some number of times. The string starts at the current cursor position and after the string is written to the screen the cursor position is updated to just after the string. Copyright 1984 Rayhawk Automation N.W. Inc P.O. Box 1427 Beaverton, Oregon 97075 Algorithm: 1) load type of crt display from 0000:463 2) load current position from 0000:0450 3) load count of characters to write 4) load character to write 5) address the screen segment 6) move string to screen segment while synchronizing with horizontal retrace 7) update cursor position CALL XREP ( FLAG% , CHARACTER$ , COUNT% , ATTRIBUTE% ) FLAG% environment flag = 0 means under basic interpreter = 1 means under compiled basic not /O = 2 means under compiled basic with /O = 3 means under compiled business basic COUNT% number of times to repeat the character CHARACTER$ character to write to screen ATTRIBUTE% attribute for character * ;______________________________________________________________________________ ; Normal assembly directives CODE SEGMENT PARA PUBLIC 'CODE' ASSUME CS:CODE EXTRN $PUTCPOS:FAR PUBLIC XREP ATTRIBUTE EQU WORD PTR [BP+6] ; address of string descriptor on stack CHAR_COUNT EQU WORD PTR [BP+8] ; address of character count on stack STRING_DESC EQU WORD PTR [BP+10] ; address of string descriptor on stack ENV_FLAG EQU WORD PTR [BP+12] ; address of environment flag on stack ;______________________________________________________________________________ XREP PROC FAR PUSH BP ; address parameters on stack MOV BP,SP PUSH AX ; save all registers used, PUSH BX PUSH CX PUSH DX PUSH SI PUSH DI PUSH ES ; ... 0) load environment flag showing compiled or interpreted MOV SI,ENV_FLAG ; load address of environment flag MOV SI,WORD PTR [SI] ; load flag itself ; ... 1) load type of crt display from 0000:463 SUB AX,AX ; address system area MOV ES,AX MOV DX,WORD PTR ES:[463h] ; load address of display adapter ADD DX,6 ; address crt status port ; ... 2) load current position from 0000:0450 if compiled ; or from DS:[0056h] if interpreted CMP SI,0 ; check environment flag JNE COMPILED MOV CX,WORD PTR DS:[0056h] ; load from basic space XCHG CL,CH ; basic has it reversed DEC CL ; basic starts count from 1 DEC CH ; instead of zero JMP SHORT CALC_POSITION COMPILED: MOV CX,WORD PTR ES:[450h] ; load current position ; from system space CALC_POSITION: SUB AH,AH ; isolate row number in AX MOV AL,CH MOV BL,80 ; multiply row by 80 bytes per row MUL BL SUB CH,CH ; add in column number ADD AX,CX MOV DI,AX SHL DI,1 ; multiply by 2 to account ; for attribute bytes ; ... 3) load count of characters to write MOV BX,CHAR_COUNT ; load address of character count MOV CX,WORD PTR DS:[BX] ; ... 4) load character to write ; note that each of the modes supported has their ; own format for the string descriptor MOV BX,STRING_DESC ; load address of string descriptor CMP SI,0 ; running compiled? JNE IS_COMPILED MOV BX,WORD PTR [BX+1] ; load offset of string JMP SHORT LOAD_CHAR IS_COMPILED: MOV BX,WORD PTR [BX+2] ; load offset of string CMP SI,3 JNE LOAD_CHAR ADD BX,3 ; Support BBC String format LOAD_CHAR: MOV AL,BYTE PTR [BX] ; load the character itself ; ... 4) load attribute for character MOV BX,ATTRIBUTE ; load address of attribute MOV BH,BYTE PTR DS:[BX] ; load the attribute itself MOV BL,AL ; move in the character ; ... 5) address the screen segment MOV AX,0B000h ; screen seg for monochrome card CMP DX,03DAh ; is this a graphic card? JNE MONOCHROME MOV AX,0B800h ; load screen seg for graphic card MONOCHROME: MOV ES,AX ; address the screen buffer ; ... 6) move string to screen while synchronizing ; with horizontal retrace DISPLAY_LOOP: CLI HSYNC_WAIT1: IN AL,DX ; check for horizontal retrace TEST AL,1 JNZ HSYNC_WAIT1 ; wait for retrace HSYNC_WAIT2: IN AL,DX ; check for horizontal retrace TEST AL,1 JZ HSYNC_WAIT2 ; wait for retrace MOV AX,BX STOSW ; store character and attribute STI CMP DI,4000 JL NOT_OFF_PAGE MOV DI,0 ; start at top again NOT_OFF_PAGE: LOOP DISPLAY_LOOP ; repeat cx times ; ... 7) update cursor position MOV AX,DI ; load current position SHR AX,1 ; discount attribute bytes SUB DX,DX ; no sign in this division MOV BX,80 ; divide by nmbr of chars per row DIV BX MOV DH,AL ; store row number ; column number already in DL MOV BH,0 ; assume page 0 MOV AH,2 ; request new position INT 10h XCHG DH,DL ; basic likes it reversed INC DL ; basic starts count from 1 INC DH ; instead of zero MOV SI,ENV_FLAG ; load address of environment flag CMP WORD PTR DS:[SI],0 ; examine flag JE NOT_COMPILED CMP WORD PTR DS:[SI],3 ; business basic? JE RET_TO_BASIC CMP WORD PTR DS:[SI],2 ; compiled with /O? JE WITH_SLASH_O ; FLAG = 1 MOV WORD PTR DS:[87h],DX ; store screen address JMP SHORT RET_TO_BASIC WITH_SLASH_O: ; FLAG = 2 MOV DI,SEG $PUTCPOS ; address put cursor routine MOV ES,DI MOV DI,OFFSET $PUTCPOS MOV DI,WORD PTR ES:[DI+2] ; load offset of cursor storage MOV WORD PTR DS:[DI],DX ; store new cursor position JMP SHORT RET_TO_BASIC NOT_COMPILED: ; FLAG = 0 MOV WORD PTR DS:[0056h],DX ; store new cursor position RET_TO_BASIC: ; FLAG = 3 POP ES POP DI POP SI POP DX POP CX POP BX POP AX POP BP RET 8 XREP ENDP ;______________________________________________________________________________ CODE ENDS END