MC68HC08AB16A Datasheet, PDF (150/380 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Freescale Semiconductor, Inc.
Monitor ROM (MON)
10.3 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
• 4800 baud to 28.8 k-baud communication with host computer
• Execution of code in RAM or ROM
10.4 Functional Description
The monitor ROM receives and executes commands from a host
computer. Figure 10-1 shows a example circuit used to enter monitor
mode and communicate with a host computer via a standard RS-232
interface.
While simple monitor commands can access any memory address, the
MCU has a ROM security feature to prevent external viewing of the ROM
contents. Proper procedures must be followed to verify ROM content.
Access to the ROM is denied to unauthorized users of customer
specified software.
In monitor mode, the MCU can execute host-computer code in RAM
while all MCU pins except PTA0 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.
Technical Data
150
MC68HC08AB16A — Rev. 2.0
Monitor ROM (MON)
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