CGB Registers - Revision history

Nitro2k01 at 02:17, 5 April 2020

2020-04-05T02:17:43Z

ISSOtm: /* Undocumented registers */ Add unofficial official names for two undocumented registers

2018-11-06T23:44:52Z

‎Undocumented registers: Add unofficial official names for two undocumented registers

ISSOtm: /* FF76 - PCM amplitudes 1 & 2 (Read Only) */ Some people threw a tantrum over this, apparently. Can you guys please wait ONE SECOND please?

2018-11-04T20:59:14Z

‎FF76 - PCM amplitudes 1 & 2 (Read Only): Some people threw a tantrum over this, apparently. Can you guys please wait ONE SECOND please?

ISSOtm: Reorganization.

2017-05-09T22:09:39Z

Reorganization.

Mantidactyle at 22:53, 4 May 2015

2015-05-04T22:53:19Z

Mantidactyle: /* FF77 - Undocumented (00h) - (Read Only) */ For better readability

2015-05-04T22:52:39Z

‎FF77 - Undocumented (00h) - (Read Only): For better readability

Mantidactyle: /* FF76 - Undocumented (00h) - (Read Only) */ For better readability

2015-05-04T22:51:49Z

‎FF76 - Undocumented (00h) - (Read Only): For better readability

LIJI at 22:10, 9 September 2014

2014-09-09T22:10:06Z

LIJI: /* FF77 - Undocumented (00h) - Always 00h (Read Only) */

2014-09-09T19:57:33Z

‎FF77 - Undocumented (00h) - Always 00h (Read Only)

Xzakox at 12:56, 28 June 2009

2009-06-28T12:56:55Z

@@ Line 1: / Line 1: @@
-{{Pandocs|cgbregisters}}
+{{Pandocs|cgb-registers}}
 ==Forward==
 This chapter describes only CGB (Color Gameboy) registers that didn't fit into normal categories - most CGB registers are described in the chapter about Video Display (Color Palettes, VRAM Bank, VRAM DMA Transfers, and changed meaning of Bit 0 of LCDC Control register). Also, a changed bit is noted in the chapter about the Serial/Link port.

@@ Line 77: / Line 77: @@
 Only bits 4, 5 and 6 of this register are read/write enabled. Their initial value is 0.
-===FF76 - PCM amplitudes 1 & 2 (Read Only)===
+===FF76 - PCM12 - PCM amplitudes 1 & 2 (Read Only)===
 This register is read-only. The low nibble is a copy of sound channel #1's PCM amplitude, the high nibble a copy of sound channel #2's.
-===FF77 - PCM amplitudes 3 & 4 (Read Only)===
+===FF77 - PCM34 - PCM amplitudes 3 & 4 (Read Only)===
 Same, but with channels 3 and 4.

@@ Line 78: / Line 78: @@
 ===FF76 - PCM amplitudes 1 & 2 (Read Only)===
-This register is read-only. The low nibble is a copy of sound channel #1's PCM amplitude, the high byte a copy of sound channel #2's.
+This register is read-only. The low nibble is a copy of sound channel #1's PCM amplitude, the high nibble a copy of sound channel #2's.
 ===FF77 - PCM amplitudes 3 & 4 (Read Only)===
 Same, but with channels 3 and 4.

@@ Line 1: / Line 1: @@
 {{Pandocs|cgbregisters}}
-===Forward===
+==Forward==
 This chapter describes only CGB (Color Gameboy) registers that didn't fit into normal categories - most CGB registers are described in the chapter about Video Display (Color Palettes, VRAM Bank, VRAM DMA Transfers, and changed meaning of Bit 0 of LCDC Control register). Also, a changed bit is noted in the chapter about the Serial/Link port.
-===Unlocking CGB functions===
+==Unlocking CGB functions==
 When using any CGB registers (including those in the Video/Link chapters), you must first unlock CGB features by changing byte 0143h in the cartridge header. Typically use a value of 80h for games which support both CGB and monochrome gameboys, and C0h for games which work on CGBs only. Otherwise, the CGB will operate in monochrome "Non CGB" compatibility mode.
-===Detecting CGB (and GBA) functions===
+==Detecting CGB (and GBA) functions==
 CGB hardware can be detected by examing the CPU accumulator (A-register) directly after startup. A value of 11h indicates CGB (or GBA) hardware, if so, CGB functions can be used (if unlocked, see above).
 When A=11h, you may also examine Bit 0 of the CPUs B-Register to separate between CGB (bit cleared) and GBA (bit set), by that detection it is possible to use 'repaired' color palette data matching for GBA displays.
 ===FF4D - KEY1 - CGB Mode Only - Prepare Speed Switch===
@@ Line 56: / Line 57: @@
 Writing a value of 01h-07h will select Bank 1-7, writing a value of 00h will select Bank 1 either.
-===FF6C - Undocumented (FEh) - Bit 0 (Read/Write) - CGB Mode Only===
+==Undocumented registers==
-===FF72 - Undocumented (00h) - Bit 0-7 (Read/Write)===
+These are undocumented CGB Registers. Purpose of these registers is unknown (if any). It isn't recommended to use them in your software, but you could, for example, use them to check if you are running on an emulator or on DMG hardware.
-===FF73 - Undocumented (00h) - Bit 0-7 (Read/Write)===
-===FF74 - Undocumented (00h) - Bit 0-7 (Read/Write) - CGB Mode Only===
-===FF75 - Undocumented (8Fh) - Bit 4-6 (Read/Write)===
-===FF76 - Undocumented (00h) - (Read Only)===
-PCM amplitude, channels 1 and 2.
-===FF77 - Undocumented (00h) - (Read Only)===
+===FF6C - Bit 0 (Read/Write) - CGB Mode Only===
-PCM amplitude, channels 3 and 4.
+Only the least significant bit of this register can be written to. It defaults to 0, so this register's initial value is $FE.
-These are undocumented CGB Registers. The numbers in brackets () indicate the initial values. Purpose of these registers is unknown (if any). Registers FF6C and FF74 are always FFh if the CGB is in Non CGB Mode. Each of the four nibbles in registers FF76-FF77 represent the current PCM amplitude (00h-0Fh) in each of the four sound channels, where the lower nibble of FF76 represents the channel 1 and the higher nibble in FF77 represents channel 4.
+===FF72 - Bits 0-7 (Read/Write)===

@@ Line 62: / Line 62: @@
 ===FF75 - Undocumented (8Fh) - Bit 4-6 (Read/Write)===
 ===FF76 - Undocumented (00h) - (Read Only)===
-PCM amplitude, channel 1 and 2
+PCM amplitude, channels 1 and 2.
 ===FF77 - Undocumented (00h) - (Read Only)===
-PCM amplitude, channel 3 and 4.
+PCM amplitude, channels 3 and 4.
 These are undocumented CGB Registers. The numbers in brackets () indicate the initial values. Purpose of these registers is unknown (if any). Registers FF6C and FF74 are always FFh if the CGB is in Non CGB Mode. Each of the four nibbles in registers FF76-FF77 represent the current PCM amplitude (00h-0Fh) in each of the four sound channels, where the lower nibble of FF76 represents the channel 1 and the higher nibble in FF77 represents channel 4.

← Older revision		Revision as of 22:52, 4 May 2015
Line 65:		Line 65:

	===FF77 - Undocumented (00h) - (Read Only)===		===FF77 - Undocumented (00h) - (Read Only)===
		+	PCM amplitude, channel 3 and 4.
		+
		+
	These are undocumented CGB Registers. The numbers in brackets () indicate the initial values. Purpose of these registers is unknown (if any). Registers FF6C and FF74 are always FFh if the CGB is in Non CGB Mode. Each of the four nibbles in registers FF76-FF77 represent the current PCM amplitude (00h-0Fh) in each of the four sound channels, where the lower nibble of FF76 represents the channel 1 and the higher nibble in FF77 represents channel 4.		These are undocumented CGB Registers. The numbers in brackets () indicate the initial values. Purpose of these registers is unknown (if any). Registers FF6C and FF74 are always FFh if the CGB is in Non CGB Mode. Each of the four nibbles in registers FF76-FF77 represent the current PCM amplitude (00h-0Fh) in each of the four sound channels, where the lower nibble of FF76 represents the channel 1 and the higher nibble in FF77 represents channel 4.

← Older revision		Revision as of 12:56, 28 June 2009
Line 1:		Line 1:
		+	{{Pandocs\|cgbregisters}}
	===Forward===		===Forward===
	This chapter describes only CGB (Color Gameboy) registers that didn't fit into normal categories - most CGB registers are described in the chapter about Video Display (Color Palettes, VRAM Bank, VRAM DMA Transfers, and changed meaning of Bit 0 of LCDC Control register). Also, a changed bit is noted in the chapter about the Serial/Link port.		This chapter describes only CGB (Color Gameboy) registers that didn't fit into normal categories - most CGB registers are described in the chapter about Video Display (Color Palettes, VRAM Bank, VRAM DMA Transfers, and changed meaning of Bit 0 of LCDC Control register). Also, a changed bit is noted in the chapter about the Serial/Link port.