Advance Information MC68HC908MR16/MC68HC908MR32 — Rev. 4.0
196 Monitor ROM (MON) MOTOROLA
Monitor ROM (MON)
10.4.6 Baud Rate
With a 4.9152-MHz crystal and the PTC2 pin at logic 1 during reset,
data is transferred between the monitor and host at 4800 baud. If the
PTC2 pin is at logic 0 during reset, the monitor baud rate is 9600. See
Table 10-9.
10.5 Security
A security feature discourages unauthorized readi ng of FLASH locations
while in monitor mode. The host can bypass the security feature at
monitor mode entry by sending eight security bytes that match the bytes
at locations $FFF6–$FFFD. Locations $FFF6–$FFFD contain
user-defined data.
NOTE: Do not leave locations $FFF6–$FFFD blank. For security reasons,
program locations $FFF6–$FFFD even if they are not used for vectors.
During monitor mode entry, the MCU waits after the power-on reset for
the host to send the eight security bytes on pin PTA0. If the received
bytes match those at locations $FFF6–$FFFD, the host bypasses the
security feature and can read all FLASH locations and execute code
from FLASH. Security remains bypassed until a power-on reset occurs.
If the reset was not a power-on reset, security remains bypassed and
security code entry is not required. (See Figure 10-6.)
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
FLASH location returns an invalid value and trying to execute code from
FLASH causes an illegal address reset. After receivin g the eight security
bytes from the host, the MCU transmits a break character, sign ifying that
it is ready to receive a command.
NOTE: The MCU does not transmit a break character until after the host sends
the eight security bytes.
Table 10-9. Monitor Baud Rate Selection
VCO Frequency Multiplier (N)
123456
Monitor baud rate 4800 9600 14,400 19,200 24,000 28,800