MC68HC12 MOTOROLA [Motorola, Inc], MC68HC12 Datasheet - Page 97

• Manufacturer Part Number: MC68HC12
• Description: The MC68HC912DT128A microcontroller unit (MCU) is a 16-bit device composed of standard on-chip peripherals including a 16-bit central processing unit
• Manufacturer: MOTOROLA [Motorola, Inc]

MC68HC912DT128A — Rev 4.0
MOTOROLA
NDRF — Narrow Data Bus for Register-Following Map Space
RFSTR1, RFSTR0 — Register Following Stretch
EXSTR1, EXSTR0 — External Access Stretch
This bit enables a narrow bus feature for the 1K byte Register-
Following Map. This is useful for accessing 8-bit peripherals and
allows 8-bit and 16-bit external memory devices to be mixed in a
system. In Expanded Narrow (eight bit) modes, Single Chip Modes,
and Peripheral mode, this bit has no effect.
The Register-Following space is mapped from $0400 to $07FF after
reset, which is next to the register map. If the registers are moved this
space follows.
This two bit field determines the amount of clock stretch on accesses
to the 1K byte Register Following Map. It is valid regardless of the
state of the NDRF bit. In Single Chip and Peripheral Modes this bit
has no meaning or effect.
This two bit field determines the amount of clock stretch on accesses
to an external address space. In Single Chip and Peripheral Modes
this bit has no meaning or effect.
0 = Makes Register-Following MAP space act as a full 16 bit data
1 = Makes the Register-Following MAP space act the same as an
bus.
8 bit only external data bus (data only goes through port A
externally).
RFSTR1
Table 6-5. RFSTR Stretch Bit Definition
Resource Mapping
0
0
1
1
RFSTR0
0
1
0
1
Miscellaneous System Control Register
Number of E Clocks
Stretched
0
1
2
3
Resource Mapping
Technical Data
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