FNX6809 Manuals

MMU Registers

Address	R/W	Name	7	6	5	4	3	2	1	0
$FFA0	RW	MMU_MEM_CTRL	-	-	EDIT_LUT		-	-	ACT_LUT
$FFA1	RW	MMU_IO_CTRL	-	-	-	-	-		$FFF0-$FFFF Enable	$FD00-$FDFF Enable

There are 4 MLUTs (MMU Lookup Tables).

ACT_LUT these two bits specify which MLUT (0–3) is used to translate CPU bus address to system bus addresses.

EDIT_LUT these two bits will specify which MLUT (0 - 3) is being edited and will appear in memory addresses $FFA8-$FFAF.

These locations are defined in nitros9/defs/f256.d:

MMU_MEM_CTRL    equ       $FFA0

MMU_IO_CTRL        equ       $FFA1

MMU_SLOT_0          equ       $FFA8               $0000-$1FFF

MMU_SLOT_1          equ       $FFA9               $2000-$3FFF

MMU_SLOT_2          equ       $FFAA               $4000-$5FFF

MMU_SLOT_3          equ       $FFAB               $6000-$7FFF

MMU_SLOT_4          equ       $FFAC               $8000-$9FFF

MMU_SLOT_5          equ       $FFAD               $A000-$BFFF

MMU_SLOT_6          equ       $FFAE               $C000-$DFFF

MMU_SLOT_7          equ       $FFAF               $E000-$FFFF

* MMU_IO_CTRL bits

* $FFA1 has 2 bits:

*    FFA1[0] =

*        1 = Enable internal RAM for segment $FD00-$FDFF.

*        0 = Disable; RAM/FLASH is accessible.

*

*    FFA1[1] =

*        1 = Enable internal RAM for segment $FFF0-$FFFF

*        0 = Disable; RAM/FLASH is accessible.

* When enabled, the areas supersede RAM/flash, but will be disabled by RESET. When the system resets,

* those regions revert to RAM/flash. Also at RESET, the contents of RAM retain the old values until the

* system powers off.

NOTE: If you are writing an OS9 program, use F$MapBlk and F$ClrBlk instead of directly accessing these addresses.