mc68hc908gr8a Freescale Semiconductor, Inc, mc68hc908gr8a Datasheet - Page 221

• Manufacturer Part Number: mc68hc908gr8a
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

18.3 Monitor Module (MON)
The monitor module allows debugging and programming of the microcontroller unit (MCU) through a
single-wire interface with a host computer. Monitor mode entry can be achieved without use of the higher
test voltage, V
requirements for in-circuit programming.
Features of the monitor module include:
18.3.1 Functional Description
Figure 18-9
The monitor module receives and executes commands from a host computer.
Figure 18-10
a host computer via a standard RS-232 interface.
Simple monitor commands can access any memory address. In monitor mode, the MCU can execute
code downloaded into RAM by a host computer while most MCU pins retain normal operating mode
functions. All communication between the host computer and the MCU is through the PTA0 pin. A
level-shifting and multiplexing interface is required between PTA0 and the host computer. PTA0 is used
in a wired-OR configuration and requires a pullup resistor.
Table 18-1
must be entered after a power-on reset (POR) and will allow communication at 9600 baud provided one
of the following sets of conditions is met:
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
unauthorized users.
Freescale Semiconductor
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Normal user-mode pin functionality
One pin dedicated to serial communication between MCU and host computer
Standard non-return-to-zero (NRZ) communication with host computer
Standard communication baud rate
Execution of code in random-access memory (RAM) or FLASH
FLASH memory security feature
FLASH memory programming interface
Monitor mode entry without high voltage, V
$FF)
Normal monitor mode entry if V
If $FFFE and $FFFF do not contain $FF (programmed state):
–
–
If $FFFE and $FFFF contain $FF (erased state):
–
–
The external clock is 9.8304 MHz
IRQ = V
The external clock is 9.8304 MHz
IRQ = V
shows the pin conditions for entering monitor mode. As specified in the table, monitor mode
shows a simplified diagram of the monitor mode.
and
TST
, as long as vector addresses $FFFE and $FFFF are blank, thus reducing the hardware
Figure 18-11
TST
DD
(this can be implemented through the internal IRQ pullup)
MC68HC908GR8A • MC68HC908GR4A Data Sheet, Rev. 5
show example circuits used to enter monitor mode and communicate with
TST
(1)
is applied to IRQ
TST
, if reset vector is blank ($FFFE and $FFFF contain
Monitor Module (MON)
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