MC68HC711xxxx Motorola, MC68HC711xxxx Datasheet - Page 44

• Manufacturer Part Number: MC68HC711xxxx
• Description: Microcontrollers
• Manufacturer: Motorola

Operating Modes and On-Chip Memory
2.3.1 RAM and Input/Output Mapping
Data Sheet
44
Hardware priority is built into RAM and I/O mapping. Registers have priority over
RAM and RAM has priority over ROM. When a lower priority resource is mapped
at the same location as a higher priority resource, a read/write of a location results
in a read/write of the higher priority resource only. For example, if both the register
block and the RAM are mapped to the same location, only the register block will be
accessed. If RAM and ROM are located at the same position, RAM has priority.
The fully static RAM can be used to store instructions, variables, and temporary
data. The direct addressing mode can access RAM locations using a 1-byte
address operand, saving program memory space and execution time, depending
on the application.
RAM contents can be preserved during periods of processor inactivity by two
methods, both of which reduce power consumption. They are:
The bootloader program is contained in the internal bootstrap ROM. This ROM,
which appears as internal memory space at locations $BF00–$BFFF, is enabled
only if the MCU is reset in special bootstrap mode.
1. In the software-based stop mode, the clocks are stopped while V
2. In the second method, the MODB/V
the MCU. Because power supply current is directly related to operating
frequency in CMOS integrated circuits, only a very small amount of leakage
exists when the clocks are stopped.
battery backup or from a second power supply.
standby voltage circuit for a standard 5-volt device. Adjustments to the
circuit must be made for devices that operate at lower voltages. Using the
MODB/V
a significant amount of external circuitry is operating from V
used to maintain RAM contents, reset must be held low whenever V
below normal operating level. Refer to
Figure 2-8. RAM Standby MODB/V
Operating Modes and On-Chip Memory
STBY
4.8-V
NiCd
pin may require external hardware, but can be justified when
V
DD
+
V
V
DD
BATT
MAX
690
V
OUT
STBY
Section 5. Resets and
4.7 k
pin can supply RAM power from a
STBY
Figure 2-8
Connections
TO MODB/V
OF M68HC11
M68HC11E Family — Rev. 5
STBY
shows a typical
DD
. If V
Interrupts.
DD
MOTOROLA
STBY
powers
DD
is
is