Datasheet

Monitor ROM (MON)
Security
MC68HC908GR8 — Rev 4.0 Technical Data
MOTOROLA Monitor ROM (MON) 203
Figure 15-8. Monitor Mode Entry Timing
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 receiving the eight security
bytes from the host, the MCU transmits a break character, signifying 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.
To determine whether the security code entered is correct, check to see
if bit 6 of RAM address $40 is set. If it is, then the correct security code
has been entered and FLASH can be accessed.
BYTE 1
BYTE 1 ECHO
BYTE 2
BYTE 2 ECHO
BYTE 8
BYTE 8 ECHO
COMMAND
COMMAND ECHO
PA0
PA1
RST
V
DD
4096 + 32 CGMXCLK CYCLES
24 BUS CYCLES
256 BUS CYCLES (MINIMUM)
1
4
1
1
2
1
BREAK
NOTES:
2 = Data return delay, 2 bit times
4 = Wait 1 bit time before sending next byte.
4
FROM HOST
FROM MCU
1 = Echo delay, 2 bit times
Frees
cale Semiconductor,
I
Freescale Semiconductor, Inc.
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