XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 220

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

Monitor ROM (MON)
14.4.8 Security
Technical Data
220
NOTE:
A security feature discourages unauthorized reading 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.
Do not leave locations $FFF6–$FFFD blank. For security reasons,
program locations $FFF6–$FFFD even if they are not used for vectors.
If FLASH is unprogrammed, the eight security byte values to be sent are
$FF, the unprogrammed state of FLASH.
During monitor mode entry, the MCU waits after the power-on reset for
the host to send the eight security bytes on pin PA0.
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. After the host bypasses security, any reset other than a
power-on reset requires the host to send another eight bytes. If the reset
V
RST
NOTE: 1 = Echo delay (2 bit times)
DD
PA0
2 = Data return delay (2 bit times)
4 = Wait 1 bit time before sending next byte.
Figure 14-6. Monitor Mode Entry Timing
FROM HOST
Monitor ROM (MON)
FROM MCU
4096 + 32 CGMXCLK CYCLES
1
24 BUS CYCLES (MINIMUM)
4
1
MC68HC908AZ60A — Rev 2.0
1
2
4
MOTOROLA
1