mc68hc908jw32 Freescale Semiconductor, Inc, mc68hc908jw32 Datasheet - Page 91

• Manufacturer Part Number: mc68hc908jw32
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Chapter 7
Monitor ROM (MON)
7.1 Introduction
This section describes the monitor ROM (MON). The monitor ROM allows complete testing of the MCU
through a single-wire interface with a host computer.
7.2 Features
Features of the monitor ROM include:
7.3 Functional Description
The monitor ROM receives and executes commands from a host computer.
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.
The monitor code allows enabling the PLL to generate the internal clock, provided the reset vector is
blank, when the device is being clocked by a low-frequency crystal. This entry method, which is enabled
when IRQ is held low out of reset, is intended to support serial communication/ programming at 9600 baud
in monitor mode.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or copying the ROM difficult for
Freescale Semiconductor
unauthorized users.
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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 ROM
ROM memory security feature
960 bytes monitor ROM code size ($FC00–$FDFF and $FE10–$FFCE)
Standard monitor mode entry if high voltage, V
MC68HC908JW32 Data Sheet, Rev. 5
(1)
TST
, is applied to IRQ
Figure 7-1
shows an example
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