MC68HC08AB16A Datasheet, PDF (159/380 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Monitor ROM (MON)
Security
10.5 Security
A security feature discourages unauthorized reading of ROM 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 ROM locations and execute code from
ROM. 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.)
V_DD
RST
4096 + 32 CGMXCLK CYCLES
256 BUS CYCLES (MINIMUM)
PTA0
FROM HOST
FROM MCU
1
4
1
12
41
NOTES:
1 = Echo delay, 2 bit times
2 = Data return delay, 2 bit times
4 = Wait 1 bit time before sending next byte.
Figure 10-6. Monitor Mode Entry Timing
MC68HC08AB16A — Rev. 2.0
MOTOROLA
Monitor ROM (MON)
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Technical Data
159