M68HC08 datasheet(75/172 Pages) FREESCALE

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MC68HC908JL3E Family Data Sheet, Rev. 3

Freescale Semiconductor

Chapter 7

Monitor ROM (MON)

7.1 Introduction

This section describes the monitor ROM (MON) and the monitor mode entry methods. The monitor ROM

allows complete testing of the MCU through a single-wire interface with a host computer. This mode is

also used for programming and erasing of FLASH memory in the MCU. Monitor mode entry can be

achieved without use of the higher test voltage, VDD +VHI, as long as vector addresses $FFFE and

$FFFF are blank, thus reducing the hardware requirements for in-circuit programming.

7.2 Features

Features of the monitor ROM include the following:

•

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 RAM or FLASH

•

FLASH memory security feature(1)

•

FLASH memory programming interface

•

960 bytes monitor ROM code size

•

Monitor mode entry without high voltage, VDD +VHI, if reset vector is blank ($FFFE and $FFFF

contain $FF)

•

Standard monitor mode entry if high voltage, VDD +VHI, is applied to IRQ1

7.3 Functional Description

The monitor ROM receives and executes commands from a host computer. Figure 7-1 shows a example

circuit used to enter monitor mode and communicate with a host computer via a standard RS-232

interface.

Simple monitor commands can access any memory address. In monitor mode, the MCU can execute

host-computer code in RAM while most MCU pins retain normal operating mode functions. All

communication between the host computer and the MCU is through the PTB0 pin. A level-shifting and

multiplexing interface is required between PTB0 and the host computer. PTB0 is used in a wired-OR

configuration and requires a pull-up resistor.

1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading or copying the FLASH difficult for

unauthorized users.

M68HC08 Datasheet(PDF) 75 Page - Freescale Semiconductor, Inc

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