MC68HC08AZ16 Datasheet, PDF (147/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Monitor ROM (MON)
Monitor
Baud
Rate
Table 9. Monitor baud rate selection
VCO Frequency Multiplier (N)
1
2
3
4
5
4800
9600
14,400
19,200
24,000
6
28,800
Security
A security feature discourages unauthorized reading of EPROM
locations while in monitor mode. The host can bypass the security
feature at monitor mode entry by sending eight security bytes that match
the byte 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. If
ROM is unprogrammed, the eight security byte values to be sent are
$FF, the unprogrammed state of ROM.
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 EPROM locations and
execute code from EPROM. 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
was not a power-on reset, security remains bypassed regardless of the
data that the host sends.
If the received bytes do not match the dta at locations $FFF6-$FFFD, the
host fails to bypass the security feature. The MCU remains in monitor
mode, but reading EPROM locations returns undefined data, and trying
to execute code from EPROM causes an illegal address reset. After the
host fails to bypass security, any reset other than a power-on reset
causes an endless loop of illegal address resets.
After reveiving the eight security bytes from the host, the MCU transmits
a break character signalling that it is ready to receive a command.
MC68HC08AZ32
146
Monitor ROM (MON)
10-mon
MOTOROLA