MC68HC908KX8 Datasheet, PDF (256/310 Pages) Motorola, Inc – Microcontrollers

Monitor ROM (MON)
18.3 Features
Features of the monitor ROM include:
• 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⁽¹⁾
• FLASH memory programming interface
• Monitor mode entry without high voltage, V_TST, if reset vector is
blank ($FFFE and $FFFF contain $FF)
• Standard monitor mode entry if high voltage, V_TST, is applied to
IRQ
18.4 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.
18.5 Monitor Mode Entry
There are two methods for entering monitor mode. The first is the
traditional M68HC08 method where V_TST is applied to IRQ1 and the
1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading
or copying the FLASH difficult for unauthorized users.
Technical Data
256
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
Monitor ROM (MON)
MOTOROLA