MC68HC908JW32_09 Datasheet, PDF (96/232 Pages) Freescale Semiconductor, Inc – M68HC08 Microcontrollers

Monitor Mode (MON)
Enter monitor mode with pin configuration shown in Figure 7-1 by pulling RST low and then high. The
rising edge of RST latches monitor mode. Once monitor mode is latched, the values on the specified pins
can change (except for PTA1, where it should be held until after security, see 7.4 Security).
Once out of reset, the MCU waits for the host to send eight security bytes. (See 7.4 Security.) After the
security bytes, the MCU sends a break signal (10 consecutive logic 0s) to the host, indicating that it is
ready to receive a command.
In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt), and break interrupt
than those for user mode. The alternate vectors are in the $FE page instead of the $FF page and allow
code execution from the internal monitor firmware instead of user code.
NOTE
Exiting monitor mode after it has been initiated by having a blank reset
vector requires a power-on reset (POR). Pulling RST low will not exit
monitor mode in this situation.
Table 7-2 summarizes the differences between user mode and monitor mode vectors.
Table 7-2. Mode Differences (Vectors)
Modes
User
Monitor
Reset
Vector
High
$FFFE
$FEFE
Reset
Vector
Low
$FFFF
$FEFF
Functions
Break
Vector
High
Break
Vector
Low
$FFFC $FFFD
$FEFC $FEFD
SWI
Vector
High
$FFFC
$FEFC
SWI
Vector
Low
$FFFD
$FEFD
7.3.2 Data Format
Communication with the monitor ROM is in standard non-return-to-zero (NRZ) mark/space data format.
Transmit and receive baud rates must be identical.
START
BIT BIT 0
BIT 1
BIT 2 BIT 3 BIT 4 BIT 5 BIT 6 BIT 7
Figure 7-2. Monitor Data Format
NEXT
START
STOP BIT
BIT
7.3.3 Break Signal
A start bit (logic 0) followed by nine logic 0 bits is a break signal. When the monitor receives a break signal,
it drives the PTA0 pin high for the duration of two bits and then echoes back the break signal.
MISSING STOP BIT
2-STOP BIT DELAY BEFORE ZERO ECHO
01234567
01234567
Figure 7-3. Break Transaction
MC68HC908JW32 Data Sheet, Rev. 6
96
Freescale Semiconductor