mc68hc908kx8 Freescale Semiconductor, Inc, mc68hc908kx8 Datasheet - Page 174

• Manufacturer Part Number: mc68hc908kx8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Development Support
16.3 Monitor ROM (MON)
The monitor ROM allows complete testing 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
in-circuit programming.
Features include:
16.3.1 Functional Description
The monitor ROM receives and executes commands from a host computer via a standard RS-232
interface. Simple monitor commands can access any memory address. In monitor mode, the
microcontroller unit (MCU) can execute host-computer code in RAM while all 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.
16.3.1.1 Monitor Mode Entry
There are two methods for entering monitor mode. The first is the traditional M68HC08 method where
V
in-circuit programming applications, will force entry into monitor mode without requiring high voltage on
the IRQ1 pin when the reset vector locations of the FLASH are erased ($FF).
Both of these methods require that the PTA1 pin be pulled low for the first 24 CGMXCLK cycles after the
part comes out of reset. This check is used by the monitor code to configure the MCU for serial
communication.
16.3.1.2 Normal Monitor Mode
Normal monitor mode is useful for MCU evaluation, factory testing, and development tool programming
operation.
conditions for entering this mode.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the FLASH difficult for
174
TST
TST
unauthorized users.
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, as long as vector addresses $FFFE and $FFFF are blank, thus reducing hardware requirements for
is applied to IRQ1 and the mode pins are configured appropriately. A second method, intended for
Normal user-mode pin functionality
One pin dedicated to serial communication between monitor ROM and host computer
Standard mark/space non-return-to-zero (NRZ) communication with host computer
Execution of code in random-access memory (RAM) or FLASH
FLASH memory security
FLASH memory programming interface
Monitor mode entry without high voltage, V
$FF)
Standard monitor mode entry if high voltage, V
Figure 16-9
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 Data Sheet, Rev. 2.1
shows an example circuit used for normal monitor mode.
(1)
TST
, if reset vector is blank ($FFFE and $FFFF contain
TST
, is applied to IRQ
Table 16-1
Freescale Semiconductor
shows the pin