gbdk-2020 | GameBoy Development Kit |
| download: https://git.y1.nz/archives/gbdk.tar.gz | |
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gbdk-lib/libc/targets/sm83/display_off.s
1 .include "global.s"
2
3 .title "display off"
4 .module Display
5
6 .area _HOME
7
8 .display_off::
9 _display_off::
10 ;; Check if the screen is on
11 LDH A, (rLCDC)
12 AND #LCDCF_ON
13 RET Z ; Return if screen is off
14 1$: ; We wait for the *NEXT* VBL
15 LDH A, (rLY)
16 CP #0x92 ; Smaller than or equal to 0x91?
17 JR NC,1$ ; Loop until smaller than or equal to 0x91
18 2$:
19 LDH A, (rLY)
20 CP #0x91 ; Bigger than 0x90?
21 JR C, 2$ ; Loop until bigger than 0x90
22
23 LDH A, (rLCDC)
24 AND #~LCDCF_ON
25 LDH (rLCDC),A ; Turn off screen
26 RET
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