M68HC11
REFERENCE MANUAL
CONFIGURATION AND MODES OF OPERATION
MOTOROLA
3-5
or special bootstrap). This restriction is accomplished by forcing the MDA control bit to
zero rather than allowing it to follow the MODA pin level at the rising edge of RESET.
By disallowing expanded modes, a software pirate is prevented from seeing the data
in EEPROM or RAM because there is no external address/data bus in single-chip
modes.
The software pirate can see what is in the on-chip ROM by disabling the security op-
tion, which can only be accomplished after the contents of EEPROM and RAM have
been erased. When a secured part is reset in bootstrap mode, the firmware in the
small bootloader program will not proceed with bootloading until the EEPROM, RAM,
and CONFIG register have been successfully erased. When a secured part is operat-
ed in normal single-chip mode, the user’s program in ROM is responsible for keeping
the MCU secured. The CONFIG register in current versions of the MC68HC11A8 can-
not be altered except in special bootstrap and special test modes.
NOCOP — COP Watchdog System Disabled
The default erased state of this bit corresponds to COP system off.
1 = The COP system is disabled and does not generate system resets.
0 = The COP system is enabled as the MCU comes out of reset.
A software service mechanism must be periodically completed prior to COP time-out
to avoid a system reset. This service will only occur at the proper repeating rate if the
software is executing in the expected, orderly fashion. If a software failure occurs, the
watchdog will time out and will generate a system reset to force the MCU to return to
proper operation. The COP watchdog mechanism is discussed in detail in
SECTION
5 RESETS AND INTERRUPTS
.
ROMON — Enable On-Chip ROM
The default erased state of this bit corresponds to ROM enabled.
1 = The 8-Kbyte on-chip program memory is enabled.
0 = The 8-Kbyte ROM is disabled and takes no space in the memory map.
In the normal single-chip operating mode, this control bit is overridden so that ROM is
always enabled. In expanded modes, turning off the ROM with this bit allows the reset
and interrupt vectors to be fetched from external memories; therefore, the user need
not know where vectors should point at the time the MCU is manufactured.
EEON — Enable On-Chip EEPROM
The default erased state of this bit corresponds to EEPROM enabled.
1 = The 512-byte on-chip EEPROM memory enabled at locations $B600–$B7FF.
0 = The 512-byte EEPROM is disabled and takes no space in the memory map.
Some versions of the M68HC11 Family have additional control bits in this register. For
example, the MC68HC811A2 uses the upper four bits to remap its 2-Kbyte EEPROM
to the upper half of any 4-Kbyte page of memory. This reference manual is based pri-
marily on the MC68HC11A8; specific information about other family members can be
found in the technical summaries.
The erased state of CONFIG is $0F on an MC68HC11A8. The MC68HC11A1 is the
same die as the MC68HC11A8 but comes from the factory with $0D in CONFIG to dis-
able the internal 8-Kbyte masked ROM. Similarly, the MC68HC11A0 version of the
part comes with $0C in CONFIG to disable both the 8-Kbyte ROM and 512-byte EE-
PROM. The CONFIG byte is not part of the 512-byte EEPROM. If the CONFIG register