There are several attribute control registers in the EGA/VGA and all compatible hardware.
The register we'll be working with is the Attribute Mode Register.
To access this register is different for the HGC/CGA boards than it is for EGA/VGA boards and all those that followed.
On a EGA/VGA we can program the registers using the CALL INTERRUPT(&H10, regs, regs)
The AX register should be set to &H1003 to access the Attribute Control Register, and the BX register should be set to 0 to disable the blinking state, or to 1 enabling blinking again.
On the CGA the control Attribute Control register is at &H3D8
Bit five of this register controls the blink state on the CGA. Set to 0 it then blinking is enabled. When set to 1 blinking is disabled.
On the HGC display this register is at &H3B8, also using bit 5 of that register.
Since the control registers on both the HGC/CGA cards can both be handled with a simple OUT statement we don't need to call an interrupt for these boards.
The example code still works well with QB45/PDS7 in a COMMAND, CMD shell, and in DOSBOX. The standard QB.QLB/QBX.QLB was used to test this using my HP Pavilion zv6000 laptop with Windows XP.
In case anyone is interested, it also works in FreeBASIC using the QB/QBX library.
'$INCLUDE: 'c:\dosemu\qb45\QB.BI'
This is the edited example I submitted that was published in volume 12#7 of PC-Magazine.
When the code is run it will place columns of color bars on the display using all sixteen colors in a text mode screen on the VGA/SVGA display.
Since the HGC/CGA/EGA boards are no longer in use those portions of code are there simply for reference.
I've edited the original code I wrote simply to test on WinXP and further comment the code for this posting.
Code:
DEFINT A-Z'$INCLUDE: 'c:\dosemu\qb45\QB.BI'DECLARE SUB FPrint (Text$, Row, Col, Fg, Bg) ' Simple Print routineDECLARE SUB SetBackIntens (Board, Setting) ' Main routine to change the ' blinking/intensity bit ' on Herc/CGA/EGA/VGA boardsDIM SHARED Regs AS RegType ' Required by CALL InterruptDIM Colors$(0 TO 15) ' Used for DATA and color chg ' '=-=-= Data for Color names 'DATA Bright White, Yellow, Bright Purple, Bright Red, Bright CyanDATA Bright Green, Bright Blue, Grey, White, Brown, Purple, RedDATA Cyan, Green, Blue, BlackFOR X = 0 TO 15 ' Read the Color names in READ Colors$(X)NEXTMDAHerc = 0: CGA = 1: EgaVga = 2 ' Explicit variablesBlinkOn = 0: BlinkOff = 1Title$ = "High intensity background colors in QuickBASIC 4.5"CLS ' Clear the screen and setupCALL SetBackIntens(EgaVga, BlinkOff) ' the initial blinking state ' ' Display our title 'FPrint Title$, 4, 40 - LEN(Title$) \ 2 + 1, 15, 0 ' ' Now drop down the color ' bars with opposing ' foreground/backgroundFOR Row = 1 TO 15 FOR PlaceBar = 0 TO 15 StartPos = ABS(Row - 2) + 1 Item$ = Colors$(15 - PlaceBar) IF Row <2> LEN(Item$) + 1 THEN Text$ = " " ELSE Text$ = " " + MID$(Item$, StartPos, 1) + " " END IF IF PlaceBar > 7 THEN Switch = 1 IF Switch = 1 THEN Fg = 31 - PlaceBar ELSE Fg = 15 - PlaceBar END IF Bg = PlaceBar FPrint Text$, Row + 6, 1 + PlaceBar * 5, Fg, Bg NEXT Switch = 0NEXTCOLOR 7, 0 ' Normal Fg/Bg colors againWHILE LEN(INKEY$) = 0: WEND ' Wait for a keypressCALL SetBackIntens(EgaVga, BlinkOn) ' Then restore the display ' boards blink state settingSUB FPrint (Text$, Row, Col, Fg, Bg) STATIC LOCATE Row, Col COLOR Fg, Bg PRINT Text$;END SUBSUB SetBackIntens (Board, Setting) Static CONST MDAHerc = &H3B8 'the MDA/Hercules port address CONST CGA = &H3D8 'the CGA port address IF Setting THEN 'exchange blinking for high-intensity SELECT CASE Board CASE 0 'monochrome adapter Out MDAHerc, 9 CASE 1 'CGA adapter Out CGA, 9 CASE 2 'EGA/VGA adapter Regs.ax = &H1003 Regs.bx = 0 Call Interrupt(&H10, Regs, Regs) END Select ELSE 'restore blinking (normal setting) SELECT CASE Board CASE 0 Out MDAHerc, &H29 CASE 1 Out CGA, &H29 CASE 2 Regs.ax = &H1003 Regs.bx = 1 CALL Interrupt(&H10, Regs, Regs) END SELECT END IfEND SUBI hope this helps anyone interested in programming the VGA/SVGA.
Thanks for reading
Statistics: Posted by RickWesh — Sat May 29, 2010 9:29 pm
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