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Operating Modes and On-Chip Memory
Memory Map
M68HC11E Family — Rev. 5
Data Sheet
MOTOROLA
Operating Modes and On-Chip Memory
35
configuration (CONFIG) register, programming calibration data into electrically
erasable, programmable read-only memory (EEPROM), and supporting emulation
and debugging during development.
2.2.4 Bootstrap Mode
When the MCU is reset in special bootstrap mode, a small on-chip read-only
memory (ROM) is enabled at address $BF00–$BFFF. The ROM contains a
bootloader program and a special set of interrupt and reset vectors. The MCU
fetches the reset vector, then executes the bootloader.
Bootstrap mode is a special variation of the single-chip mode. Bootstrap mode
allows special-purpose programs to be entered into internal random-access
memory (RAM). When bootstrap mode is selected at reset, a small bootstrap ROM
becomes present in the memory map. Reset and interrupt vectors are located in
this ROM at $BFC0–$BFFF. The bootstrap ROM contains a small program which
initializes the serial communications interface (SCI) and allows the user to
download a program into on-chip RAM. The size of the downloaded program can
be as large as the size of the on-chip RAM. After a 4-character delay, or after
receiving the character for the highest address in RAM, control passes to the
Use of an external pullup resistor is required when using the SCI transmitter pin
because port D pins are configured for wired-OR operation by the bootloader. In
bootstrap mode, the interrupt vectors are directed to RAM. This allows the use of
interrupts through a jump table. Refer to the application note AN1060 entitled
2.3 Memory Map
The operating mode determines memory mapping and whether external
families comprising the M68HC11 E series of MCUs.
Memory locations for on-chip resources are the same for both expanded and
single-chip modes. Control bits in the configuration (CONFIG) register allow
EPROM and EEPROM (if present) to be disabled from the memory map. The RAM
is mapped to $0000 after reset. It can be placed at any 4-Kbyte boundary ($x000)
by writing an appropriate value to the RAM and I/O map register (INIT). The 64-byte
register block is mapped to $1000 after reset and also can be placed at any 4-Kbyte
boundary ($x000) by writing an appropriate value to the INIT register. If RAM and
registers are mapped to the same boundary, the first 64 bytes of RAM will be
inaccessible.
Refer to Figure 2-7, which details the MCU register and control bit assignments.
Reset states shown are for single-chip mode only.