IBM PC CONVERTIBLE - Page 122

0463
0463
E8 0497 R
0466 26: 8A 04
0469 22 C4
046B 02 EO
0460 BA CE
046F 02 CO
0471 E9 016F R
0474
0474
0474
50
0475
50
0476
E8 0497
0479
02 E8
047B
22 C4
0470 26: 8A DC
0480 58
0481 F6 C3 80
0484 75 00
0486 F6 04
0488 22 CC
048A OA C1
048C
048C
26: 88 04
048F
58
0490 E9 016F R
0493
0493
32 C1
0495 EB F5
0497
0497
0497
53
0498
50
0499 BO 28
0498 52
049C 80 E2 FE
049F F6 E2
READ DOT -- WRITE DOT
THESE ROUTINES WILL WRITE A DOT, OR READ THE DOT AT
THE INDICATED LOCATION
ENTRY --
EXIT
ox = ROW (0-199) (THE ACTUAL VAL DEPENDS ON THE MODE)
CX COLUMN ( 0-639) ( THE VALUES ARE NOT RANGE CHECKED)
AL OOT VALUE TO WRITE (1,2 OR 4 BITS OEPENOING ON MODE,
REQ'D FOR WRITE DOT ONLY, RIGHT JUlTIFIED)
BIT 7 OF AL=l INDICATES XOR THE VAL INTO LOCATION
OS DATA SEGMENT
ES REG EN S EGM ENT
AL =
DOT VALUE READ, RIGHT JUSTIFIED, READ ONLY
--- --- - - - - - - - - -- - - - - - - - - -- - - - - - - - - - - - - - - - - - - - - -- - - - --- - -- - -- - - --
ASSUME CS: ROMCODE, OS: DATA, ES: DATA
READ_DOT PROC NEAR
CALL
R3 ; FIND BYTE POSITION OF DOT
MOV
AL,ES:-SI- GET THE BYTE
AND AL,AH
MASK OFF OTHER BITS IN BYTE
SHL AL, CL
LEFT JUSTI FY THE VALUE
MOV CL,DH
GET NUMBER OF BITS IN RESULT
ROL
AL,CL RIGHT JUSTIFY THE RESULT
JMP
VIDEO_RETURN RETURN FROM VIDEO 10
READ_DOT
ENDP
WRITE_DOT
PROC
NEAR
PUSH AX
SAVE DOT VALUE
PUSH AX TWICE
CALL R3
FIND BYTE POSITION OF DOT
SHR AL, CL
SHIFT TO SET UP OUT BITS
AND AL,AH
;
STRI P OFF THE OTHER BITS
MOV
CL,ES:-SI- GET THE CURRENT BYTE
POP
BX RECOVER XOR FLAG
TEST BL ,80H IS IT ON
JNZ R2 YES, XOR THE DOT
NOT AH SET THE MASK TO REMOVE THE
AND CL,AH INDICATED BITS
OR AL,CL OR IN THE NEW VALUE OF BITS
R1 : ; FINISH_DOT
MOV ES:-SI-,AL RESTORE THE BYTE IN MEMORY
POP AX
JMP V IDEO_RETURN RETURN FROM V IDEO 10
R2: XOR_DOT
XOR AL,CL EXCLUSIVE OR THE DOTS
JMP R1 FINISH UP THE WRITING
WRITE_DOT
ENDP
R3 PROCEDURE
THIS SUBROUTINE DETERMINES THE REGEN BYTE LOCATION
OF THE INDICATED ROW COLUMN VALUE IN GRAPHICS MODE.
ENTRY --
EXIT --
R3
DX = ROW VALUE (0-199)
CX = COLUMN VALUE (0-639)
SI 0 OFFSET INTO REGEN BUFFER FOR BYTE OF INTEREST
AH = MASK TO STRIP OFF THE BITS OF INTEREST
CL 0 BITS TO SHIFT TO RIGHT JUSTIFY THE MASK IN AH
DH = # BITS IN RESULT
PROC
NEAR
PUSH BX ; SAVE BX DURING OPERATION
PUSH
AX ; SAVE AL DURING OPERATION
DETERMINE 1ST BYTE IN INDICATED ROW BY MULTIPLY ROW VALUE BY 40
LOW BIT OF ROW DETERMINES EVEN/ODD, 80 BYTES/ROW
MOV AL,40
PUSH OX
SAVE ROW VALUE
AND DL,OFEH STRIP OFF ODD/EVEN BIT
MUL DL AX HAS ADDRESS OF 1ST BYTE
ROM BIOS 2-97