MC68HC08AB16A Datasheet, PDF (160/380 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Monitor ROM (MON)
Upon power-on reset, if the received bytes of the security code do not
match the data at locations $FFF6–$FFFD, the host fails to bypass the
security feature. The MCU remains in monitor mode, but reading a ROM
location returns an invalid value and trying to execute code from ROM
causes an illegal address reset. After receiving the eight security bytes
from the host, the MCU transmits a break character, signifying that it is
ready to receive a command.
To determine whether the security code entered is correct, check to see
if bit 6 of RAM address $50 is set. If it is, then the correct security code
has been entered and ROM can be accessed.
NOTE: The MCU does not transmit a break character until after the host sends
the eight security bits.
If the host fails the security bypass as described in 10.5 Security, the
MCU remains in monitor mode, but reading a ROM location returns an
invalid value and trying to execute code from ROM causes an illegal
address reset. The MCU monitor commands are still valid and user
software can execute from RAM; accessing I/Os and EEPROM (see
10.6 EEPROM Security).
10.6 EEPROM Security
When the EEPROM security feature is set (EEMONSEC=1 in mask
option register B), user software cannot access the EEPROM locations
in monitor mode if security bypass had failed.
10.7 Extended Security
To further disable monitor mode functions, an extended security
command keyword can be set at ROM locations $FFC0–$FFC7. The
keyword is eight bytes long with a 7-byte ASCII string and 1-byte $00
delimiter. The keyword for the MC68HC08AB16A MCU is "PSWDOPT"
+ $00.
Entry to monitor mode with extended security command keyword
programmed, the MCU stops communicating with the host after
transmitting a break character if the host fails the security bypass as
described in 10.5 Security.
Technical Data
160
MC68HC08AB16A — Rev. 2.0
Monitor ROM (MON)
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