MMU RAMROM Mode - Revision history

Tlindner: Re oranges for clarity.

2026-07-18T23:55:34Z

Re oranges for clarity.

← Older revision		Revision as of 19:55, 18 July 2026
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	Color Computer 3 Memory Management Unit in ROM/RAM		Color Computer 3 Memory Management Unit in ROM/RAM

	The ~~MMU in the CoCo 3 has access~~ to ~~64 blocks~~ of ~~RAM each 8 kilobytes in size~~. ~~In ROM/~~RAM ~~mode~~ the ~~last four blocks don't access RAM~~. ~~They access either internal or external ROM~~. ~~The RAM/~~ROM ~~mode is entered by writing any value~~ to ~~address~~ $~~FFDE~~. ~~RAM mode is selected by writing any value to address~~ $~~FFDF~~.		The ROM pages ($3C-$3F) may be written to any of the eight MMU slots. However, unlike RAM pages, the MMU ignores the lower two bits of the value written when the page refers to ROM. Instead, it replaces those bits with the lower two bits of the slot number.

			For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:

			[[image:ROMRAM.png\|center]]

	In ROM/RAM mode there are three different ROM configurations available. They are selected by setting bits 1 and 0 of address $FF90 to:		In ROM/RAM mode there are three different ROM configurations available. They are selected by setting bits 1 and 0 of address $FF90 to:
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	\|-		\|-
	\| $E000 - $FFFF		\| $E000 - $FFFF
	\| Slot 7: $~~FFA6~~, $FFAF		\| Slot 7: $FFA7, $FFAF
	\|}		\|}


	The ROM pages ($3C-$3F) can be written to any of the eight available MMU slots. In all cases the last two bits of the page are ignored by the MMU and substituted by the last two bits of the slot number.		The ROM pages ($3C-$3F) can be written to any of the eight available MMU slots. In all cases the last two bits of the page are ignored by the MMU and substituted by the last two bits of the slot number.

	~~For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:~~


	~~[[image:ROMRAM.png\|center]]~~

	This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 3 and 7.		This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 3 and 7.

AllenHuffman: adding NavArticles template (also adds category)

2008-04-16T15:02:46Z

adding NavArticles template (also adds category)

← Older revision		Revision as of 11:02, 16 April 2008
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			{{NavArticles}}
	Color Computer 3 Memory Management Unit in ROM/RAM		Color Computer 3 Memory Management Unit in ROM/RAM

Tlindner at 02:57, 2 May 2007

2007-05-02T02:57:40Z

← Older revision		Revision as of 22:57, 1 May 2007
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	For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:		For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:

	[[image:ROMRAM.png]]
			[[image:ROMRAM.png\|center]]

	This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 3 and 7.		This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 3 and 7.

Tlindner at 02:56, 2 May 2007

2007-05-02T02:56:44Z

← Older revision		Revision as of 22:56, 1 May 2007
Line 66:		Line 66:
	[[image:ROMRAM.png]]		[[image:ROMRAM.png]]

	This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 1 and 7.		This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 3 and 7.

Tlindner at 02:55, 2 May 2007

2007-05-02T02:55:18Z

← Older revision		Revision as of 22:55, 1 May 2007
Line 66:		Line 66:
	[[image:ROMRAM.png]]		[[image:ROMRAM.png]]

	This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.		This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 2 and 6; $3F in 1 and 7.

Tlindner at 02:52, 2 May 2007

2007-05-02T02:52:56Z

← Older revision		Revision as of 22:52, 1 May 2007
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	The ROM pages ($3C-$3F) can be written to any of the eight ~~avaiable~~ MMU slots. In all cases the last two bits of the page are ignored by the MMU and substituted by the last two bits of the slot number.		The ROM pages ($3C-$3F) can be written to any of the eight available MMU slots. In all cases the last two bits of the page are ignored by the MMU and substituted by the last two bits of the slot number.

	For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:		For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:

	*		[[image:ROMRAM.png]]

	This ~~essemtially~~ means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.		This essentially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.

Tlindner at 02:16, 2 May 2007

2007-05-02T02:16:45Z

@@ Line 10: / Line 10: @@
 ! $3E
 ! $3F
 |-
-| Extnd Color BASIC
+| align="center" | Extended Color BASIC
-| Color BASIC
+| align="center" | Color BASIC
-| 8K Cart ROM
+| align="center" colspan="2" | 16K Cartridge ROM
-| 8K Cart ROM
+| align="center" | 0X
 |}
-The ROM pages (3C-3F) can be written to any of the eight avaiable MMU slots. In all cases the last two bits the page page are ignored by the MMU and substituted by the last two bits of the slot number.
+The ROM pages ($3C-$3F) can be written to any of the eight avaiable MMU slots. In all cases the last two bits of the page are ignored by the MMU and substituted by the last two bits of the slot number.
 For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:
@@ Line 27: / Line 66: @@
+*
-This essemtially means that Page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.
+This essemtially means that page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.

Tlindner at 01:54, 2 May 2007

2007-05-02T01:54:59Z

@@ Line 1: / Line 1: @@
 Color Computer 3 Memory Management Unit in ROM/RAM
-The MMU in the CoCo 3 has access to 63 blocks of RAM each 8 kilobytes in size. In ROM/RAM mode the last four blocks don't access RAM. They access either internal or external ROM.
+The MMU in the CoCo 3 has access to 64 blocks of RAM each 8 kilobytes in size. In ROM/RAM mode the last four blocks don't access RAM. They access either internal or external ROM. The RAM/ROM mode is entered by writing any value to address $FFDE. RAM mode is selected by writing any value to address $FFDF.
+*

Tlindner: Composing

2007-05-02T01:45:08Z

Composing

New page

Color Computer 3 Memory Management Unit in ROM/RAM

The MMU in the CoCo 3 has access to 63 blocks of RAM each 8 kilobytes in size. In ROM/RAM mode the last four blocks don't access RAM. They access either internal or external ROM.

*

*

The ROM pages (3C-3F) can be written to any of the eight avaiable MMU slots. In all cases the last two bits the page page are ignored by the MMU and substituted by the last two bits of the slot number.

For example, writing $3D to slot 2 of the MMU does not map the second 8k page of ROM to addresses $4000-$5FFF. It maps page $3E (the third ROM page), because:

*

This essemtially means that Page $3C will only appear in slots 0 and 4; $3D in 1 and 5; $3E in 1 and 6; $3F in 1 and 7.