MC68HC812A4 Datasheet, PDF (90/342 Pages) Motorola, Inc – 16-bit device composed of standard on-chip peripheral modules connected by an intermodule bus. Modules include

Operating Modes and Resource Mapping
many as six of the standard 16 address lines. Usage of chip selects
identifies the source of the internal address.
All of the memory expansion windows have a fixed size and two of them
have a fixed address location. The third has two selectable address
locations.
Address: $0013
Bit 7
6
5
4
3
2
1
Bit 0
Read:
EWDIR NDRC
0
0
0
0
0
0
Write:
Reset: 0
0
0
0
0
0
0
0
Figure 5-5. Miscellaneous Mapping Control Register (MISC)
Read: Anytime
Write: Once in normal modes; anytime in special modes
EWDIR — Extra Window Positioned in Direct Space Bit
This bit is only valid in expanded modes. If the EWEN bit in the
WINDEF register is cleared, then this bit has no meaning or effect.
1 = If EWEN is set, then a 1 in this bit places the EPAGE at
$0000–$03FF.
0 = If EWEN is set, then a 0 in this bit places the EPAGE at
$0400–$07FF.
NDRC — Narrow Data Bus for Register Chip-Select Space Bit
This function requires at least one of the chip selects CS3–CS0 to be
enabled. It effects the external 512-byte memory space.
1 = Makes the register-following chip-selects (2, 1, 0, and
sometimes 3) active space (512-byte block) act the same as
an 8-bit only external data bus. Data only goes through port C
externally. This allows 8-bit and 16-bit external memory
devices to be mixed in a system.
0 = Makes the register-following chip-select active space act as a
full 16-bit data bus. In the narrow (8-bit) mode, NDRC has no
effect.
MC68HC812A4 — Rev. 3.0
90
Operating Modes and Resource Mapping
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