MC68HC908AP16CFB datasheet(166/440 Pages) MOTOROLA

166 / 440 page

Monitor ROM (MON)

Data Sheet

MC68HC908AP Family — Rev. 2.5

166

MOTOROLA

10.4 Security

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.

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 10-8.)

Figure 10-8. Monitor Mode Entry Timing

PTA0

RST

VDD

4096 + 32 ICLK CYCLES

256 BUS CYCLES (MINIMUM)

NOTES:

2 = Data return delay, 2 bit times.

4 = Wait 1 bit time before sending next byte.

FROM HOST

FROM MCU

1 = Echo delay, 2 bit times.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

MC68HC908AP16CFB Datasheet(PDF) 166 Page - Motorola, Inc