Terminal control/Clear the screen: Difference between revisions
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bne clearscreen
</lang>
=={{header|68000 Assembly}}==
===Neo Geo MVS===
The following will clear all hardware sprites from video memory as well as the "FIX Layer" (a simple tilemap intended for text). The registers <code>D0</code>, <code>D1</code>, and <code>A0</code> will be clobbered after returning, so keep that in mind.
<lang 68000devpac>JSR $C004C2
JSR $C004C8</lang>
===Sega Genesis===
The fastest way to do this is with direct memory access. It is assumed that your tile pattern definition has 32 null bytes starting at VRAM offset $0000. (You need to have 32 null bytes in VRAM somewhere for this to work, it doesn't have to be at VRAM address $0000, but this example uses that for convenience.) The code below also assumes the Genesis's VDP (video display processor) has been set up as follows:
* VDP register 2 = %00110000 = foreground tilemap at VRAM address $C000
* VDP register 3 = %00111100 = window tilemap at VRAM address $F000
* VDP register 4 = %00000111 = background tilemap at VRAM address $E000
* VDP register 5 = %01101100 = sprite attribute table at VRAM address $D800
This technique uses DMA fill mode to fill the tilemaps (not the pattern definitions) with transparent tiles. This has the effect of wiping the screen of all graphics, while not disturbing the tile definitions themselves.
<lang 68000devpac>dma_fill:
;input:
;D2.L = what address to write to.
;D1.W = DMA LENGTH (measured in words)
;D0 = WHAT DATA TO USE TO FILL VRAM
vdp_data equ $C00000
vdp_ctrl equ $C00004
MOVE.L #$40000003,D2 ;VDP sees this as VRAM address $C000
MOVE.W #$2000,D1 ;fill $2000 words ($4000 bytes)
MOVEQ #0,D0 ;with zeroes.
MOVE SR,-(SP)
MOVEM.L D3-D7,-(SP)
MOVE #$2700,SR ;disable interrupts
MOVEQ.L #-109,D3 ;quickly move #$FFFFFF93 into D3
LSL.W #8,D3
OR.B D1,D3
;d3 contains $93xx where xx is the low byte of dma length
;this is the correct command to give the vdp
LSR.W #8,D1 ;shift high byte of dma length down to low byte
MOVEQ.L #-108,D4 ;quickly move #$FFFFFF94 into d4
LSL.W #8,D4 ;D4 = #$FFFF9400
OR.B D1,D4
;d3 contains $94xx where xx is the high byte of dma length
;this is the correct command to give the vdp
OR.L #$20,D2 ;tells the vdp the next write is a DMA write
.wait:
move.w VDP_ctrl,d7
and.w #%0000000000001000,d7 ;See if vblank is running
bne .wait ;wait until it is
MOVE.W #($8100|%01110100),(VDP_CTRL) ;ENABLE DMA
move.w #$8F01,(vdp_ctrl) ;set auto-inc to 1
MOVE.W #$9780,(vdp_ctrl) ;enable dma vram fill
MOVE.W D3,(vdp_ctrl) ;set dma length low byte
MOVE.W D4,(vdp_ctrl) ;set dma length high byte
MOVE.L D2,(vdp_ctrl) ;set destination address
MOVE.W D0,(vdp_data)
;at this point the 68000 halts until DMA is finished.
move.w #($8100|%01100100),(VDP_CTRL) ;DISABLE DMA
move.w #$8F02,(vdp_ctrl) ;set auto-inc back to 2
MOVEM.L (SP)+,D3-D7
RTR</lang>
=={{header|8080 Assembly}}==
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