Technical information

AN2317/D
4 Low-Cost Programming and Debugging Options for M68HC08 MCUs
MOD1, MOD0 The mode select pins must be at their prescribed levels if the V
TST
voltage is
applied to the IRQ pin. These pins select monitor mode. They are also used by
Motorola production test facilities and emulator manufacturers to gain access
to special test and emulation features.
DIV4 DIV4 (for bus clock equal to input clock divided by 4), if implemented, is used
by the monitor firmware to determine the appropriate communications baud
rate. A high-frequency input clock is recommended for the MON08 interface,
which necessitates pulling the DIV4 signal high.
SSEL SSEL (for serial select), if implemented, allows serial or parallel entry of
security code bytes. Serial entry is the normal entry method supported by
programming and debugging tools. Parallel entry is only useful during
production test, and is not a user option, since eight more pins are needed to
enter the security data. This signal does not allow memory data to be loaded
into the FLASH in a parallel mode.
OSC Since the monitor serial communication is generated by the monitor mode
firmware rather than a dedicated serial communications interface, the internal
bus clock must be forced to a frequency that will yield baud rates that personal
computers can recognize. The OSC1 input can be over-driven by a canned
oscillator even if a crystal resonator circuit or RC network is connected to the
OSC1 and OSC2 pins. While most M68HC08 monitor mode implementations
recommend a 9.8304 MHz oscillator input to get a 9600 baud rate, some
M68HC08’s, particularly the M68HC(9)08A and M68HC(9)08JB Families,
specify other oscillator frequencies. Again, refer to the specific data sheet for
details.
Reset
The Reset input is required for proper debugging operation, but is not required
for programming and simple debugging. The Reset
pin normally is pulled up
(via an internal pullup resistor) to V
DD
. In monitor mode on some devices, this
pin can be raised to the V
TST
level (after monitor mode is entered) to allow the
IRQ
pin to be switched back to its interrupt input function for debugging
purposes. For example, the M68HC908KX Family requires a pullup on the I/O
pin that is shared with Reset
.
Ground/V
SS
The V
SS
pin must be connected to the host system’s ground to provide the
proper voltage reference for communications and mode biasing.
Freescale Semiconductor, I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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