From c1509b633934eb3841f61062d263a2016e7231f3 Mon Sep 17 00:00:00 2001 From: Lior Halphon Date: Tue, 13 Apr 2021 23:34:49 +0300 Subject: [PATCH] KEY0 info --- BESS.md | 1 + 1 file changed, 1 insertion(+) diff --git a/BESS.md b/BESS.md index 59ca3db2..03cb54c9 100644 --- a/BESS.md +++ b/BESS.md @@ -74,6 +74,7 @@ The values of memory-mapped registers should be written 'as-is' to memory as if * Unused registers have Don't-Care values which should be ignored * Unused register bits have Don't-Care values which should be ignored * If the model is CGB or newer, the value of KEY0 (FF4C) must be valid as it determines DMG mode + * Bit 2 determines DMG mode. A value of 0x04 usually denotes DMG mode, while a value of `0x80` usually denotes CGB mode. * Sprite priority is derived from KEY0 (FF4C) instead of OPRI (FF6C) because OPRI can be modified after booting, but only the value of OPRI during boot ROM execution takes effect * If a register doesn't exist on the emulated model (For example, KEY0 (FF4C) on a DMG), its value should be ignored. * BANK (FF50) should be 0 if the boot ROM is still mapped, and 1 otherwise, and must be valid.