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Discussion about software development for the old-school Gameboys, ranging from the "Gray brick" to Gameboy Color
(Launched in 2008)

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#1 2015-03-16 01:09:52

New member
Registered: 2015-03-16
Posts: 1

Turning LCD off outside of VBlank interval

There is this caution in Pan Docs ( … lay_Enable):

CAUTION: Stopping LCD operation (Bit 7 from 1 to 0) may be performed during V-Blank ONLY, disabeling the display outside of the V-Blank period may damage the hardware. This appears to be a serious issue, Nintendo is reported to reject any games that do not follow this rule.

However, in the official Nintendo Game Boy Programming Manual (version 1.0, released 11/09/1999) it's not mentioned that it can cause any hardware damage:

2.1.1 Setting the LCDC to OFF (Recommended)
Covers: DMG and CGB
In early DMGs, a black horizontal line appears on the screen if the LCDC is stopped (LCDC register bit 7 <- 0) at any time other than during vertical blanking. Therefore, the LCDC should be set to OFF during V-blanking. If the occurrence of V-blanking cannot be confirmed, the LCDC should be set to OFF when the value of the LY register is 145 (0x91) or greater. These restrictions do not apply in CGB. <...>

(Note that it says 'Recommended'. Some other cautions are 'Required', but not this one)

In the end, which one is correct?

Last edited by deeplinks (2015-03-16 01:58:24)



#2 2015-05-06 07:20:22

From: France
Registered: 2015-03-04
Posts: 28

Re: Turning LCD off outside of VBlank interval

Sorry I'm a bit late but you should wait for the v-blank before turning off the screen.

Another boring artist.

Current software project --> Walking under the rain (GB)
Current hardware project --> GlitchBoy



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