IBM PC CONVERTIBLE Technical Reference page 125

0533
GRAPHICS DOWN
ENTRY
EXIT
THIS ROUTINE SCROLLS DOWN THE INFORMATION ON THE CRT
CH,CL = UPPER LEFT CORNER OF REGION TO SCROLL
DH,DL = LOWER RIGHT CORNER OF REGION TO SCROLL
BOTH OF THE ABOVE ARE IN CHARACTER POSITIONS
BH = FILL VALUE FOR BLANKED LINES
AL =
#
LINES TO SCROLL (AL=O MEANS BLANK THE ENTIRE
FI ELD)
OS = DATA SEGMENT
ES = REGEN SEGMENT
NOTHING, THE SCREEN IS SCROLLED
GRAPH I CS_DOWN PROC NEAR
0533 FD STD ; SET DIRECTION
0534 8A 08
0536 8B C2
MOV BL,AL
MOV AX,DX
; SAVE LINE COUNT IN BL
; GET LOWER RIGHT POS INTO AX
;----- USE CHARACTER SUBROUTINE FOR POSITIONING
;----- ADDRESS RETURNED IS MULTIPLIED BY 2 FROM CORRECT VALUE
0538 E8
onc
R
CALL
GRAPH_POSN
053B 8B F8 MOV DI,AX ; SAVE RESULT AS DEST AD DR
DETERMINE SIZE OF WINDOW
0530 2B 01
SUB
OX, CX
053F 81 C2 OlD1 ADD DX,101H ADJUST VALUES
0543 DO E6 SAL
DH,l MUL TIPLY
#
ROWS BY 4
SINCE 8 VERT DOTS/CHAR
0545 DO E6 SAL DH,l AND EVEN/ODD ROWS
DETERMINE CRT MODE
0547 80 3£ 0049 R 06 CMP CRLMODE,6 TEST FOR MEDIUM RES
054C 73 05 JNC R12 FIND_SOURCE_DOWN
;----- MEDIUM RES DOWN
054E
DO E2
SAL DL,l
#
COLUMNS * 2, SINCE
2 BYTES/CHAR (OFFS,ET OK)
0550
01 E7
SAL 01,1 OFFSET *2 SINCE 2 BYTES/CHAR
0552
47 INC
01
PO I NT TO LAST BYT E
DETERMINE THE SOURCE ADDRESS IN THE BUFFER
0553 R12 :
FIND_SOURCLDOWN
0553 06 PUSH ES
BOTH SEGMENTS TO REGEN
0554 IF
POP
OS
05.55 2A ED
SUB CH,CH ZERO TO HIGH OF COUNT REG
0557
81 C7 OOFO ADD 01,240 POINT TO LAST ROW OF PIXELS
055B DO E3 SAL BL,l MUL TIPLY NO. OF LINES BY 4
0550 DO E3
SAL
BL,l
055F 74 2E JZ R16 IF ZERO, BLANK ENTIRE FIELD
0561 8A C3 MOV AL,BL GET NUMBER OF LINES IN AL
0563 B4 50 MOV AH,80 80 BYT ES / ROW
0565 F6 E4 MUL AH DETERMINE OFFSET TO SOURCE
0567 8B F7 MOV SI,DI SET UP SOURCE
0569 2B FO SUB SI,AX SUBTRACT THE OFFSET
056B 8A E6 MOV AH,DH NUMBER OF ROWS IN FIELD
0560 2A E3 SUB AH,BL DETERMINE NUMBER TO MOVE
LOOP THROUGH, MOVING ONE ROW AT A TIME, BOTH EVEN & ODD FI ELDS
056F R13 :
ROW_LOOP _DOWN
056F E8 0593 R CALL R17 MOVE ONE ROW
0572 81 EE 2050 SUB SI,2000H+80 MOV E TO N EXT ROW
0576 81 EF 2050 SUB DI,2000H+80
057A FE CC DEC AH NUMBER OF ROWS TO MOVE
057C 75 F1 JNZ R13 CONTINUE TILL ALL MOVED
FILL IN THE VACATED LINE(S)
2-100 ROM BIOS