MC68HC908AP16CFB datasheet(167/440 Pages) MOTOROLA

167 / 440 page

Monitor ROM (MON)

Security

MC68HC908AP Family — Rev. 2.5

Data Sheet

MOTOROLA

167

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 bits.

To determine whether the security code entered is correct, check to see

if bit 6 of RAM address $60 is set. If it is, then the correct security code

has been entered and FLASH can be accessed.

If the security sequence fails, the device should be reset by a power-on

reset and brought up in monitor mode to attempt another entry. After

failing the security sequence, the FLASH module can also be mass

erased by executing an erase routine that was downloaded into internal

RAM. The mass erase operation clears the security code locations so

that all eight security bytes become $FF (blank).

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MC68HC908AP16CFB Datasheet(PDF) 167 Page - Motorola, Inc