mc68hc908ap8a Freescale Semiconductor, Inc, mc68hc908ap8a Datasheet - Page 115

• Manufacturer Part Number: mc68hc908ap8a
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Chapter 8
Monitor Mode (MON)
8.1 Introduction
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.
8.2 Features
Features of the monitor ROM include:
8.3 Functional Description
The monitor module receives and executes commands from a host computer.
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
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.
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 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
959 bytes monitor ROM code size
($FC00–$FDFF and $FE10–$FFCE)
Monitor mode entry without high voltage, V
$FF)
Standard monitor mode entry if high voltage, V
Resident routines for in-circuit programming
TST
, as long as vector addresses $FFFE and $FFFF are blank, thus reducing the hardware
MC68HC908AP A-Family Data Sheet, Rev. 3
(1)
TST
, if reset vector is blank ($FFFE and $FFFF contain
TST
, is applied to IRQ1
Figure 8-1
shows an
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