
Functional Description
MC68HC08LK60 MC68HC908LK60 Advance Information Data Sheet, Rev. 1.1
Freescale Semiconductor
207
18.3.1 Entering Monitor Mode
Table 18-1 shows the pin conditions for entering monitor mode.
Enter monitor mode by either:
Executing a software interrupt instruction (SWI) or
Applying a logic 0 and then a logic 1 to the RST pin
The MCU sends a break signal (10 consecutive logic 0s) to the host computer, indicating that it is ready
to receive a command. The break signal also provides a timing reference to allow the host to determine
the necessary baud rate.
Monitor mode uses alternate vectors for reset, SWI, and break interrupt. 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. The COP module is disabled in monitor mode as long as VDD +VHI is applied to either the
of operation.
NOTE
Holding the PTC3 pin low when entering monitor mode causes a bypass of
a divide-by-two stage at the oscillator. The CGMOUT frequency is equal to
the CGMXCLK frequency, and the OSC1 input directly generates internal
bus clocks. In this case, the OSC1 signal must have a 50% duty cycle at
maximum bus frequency.
Table 18-2 is a summary of the differences between user mode and monitor mode.
Table 18-1. Mode Selection
IRQ1
pin
PTC0
pin
PTC1
pin
PTA0
pin
PTC3
pin
Mode
CGMOUT
Bus
frequency
VDD + VHI
1011
Monitor
or
VDD + VHI
1010
Monitor
CGMXCLK
Table 18-2. Mode Differences
Modes
Functions
COP
Reset
vector
high
Reset
vector
low
Break
vector
high
Break
vector
low
SWI
vector
high
SWI
vector
low
User
Enabled
$FFFE
$FFFF
$FFFC
$FFFD
$FFFC
$FFFD
Monitor(1)
1. If PTA0 is low out of reset, the CPU performs a jump to RAM for burn-in.
Disabled(2)
2. If the high voltage (VDD + VHI) is removed from the IRQ1 pin or the RST pin, the SIM
asserts its COP enable output.
$FEFE
$FEFF
$FEFC
$FEFD
$FEFC
$FEFD
CGMXCLK
2
-----------------------------
CGMVCLK
2
-----------------------------
CGMOUT
2
--------------------------
CGMOUT
2
--------------------------