Features - Motorola MC68HC908GP32 Technical Data Manual

Monitor ROM (MON)

15.3 Features

15.4 Functional Description
Technical Data
196
Freescale Semiconductor, Inc.
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 RAM or FLASH
• FLASH memory security feature
• FLASH memory programming interface
• Enhanced PLL (phase-locked loop) option to allow use of external
32.768-kHz crystal to generate internal frequency of 2.4576 MHz
• 307 bytes monitor ROM code size ($FE20 to $FF52)
• Monitor mode entry without high voltage, V
blank ($FFFE and $FFFF contain $FF)
• Standard monitor mode entry if high voltage, V
IRQ
The monitor ROM receives and executes commands from a host
computer. Figure 15-1
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
1. No security feature is absolutely secure. However, Motorola's strategy is to make reading or
copying the FLASH difficult for unauthorized users.
Monitor ROM (MON)
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1
shows an example circuit used to enter monitor
MC68HC908GP32
, if reset vector is
TST
, is applied to
TST
MC68HC08GP32 Rev. 6
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MOTOROLA