Freescale Semiconductor, Inc.
Monitor ROM (MON)
13.3 Features
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
• 4800 baud–28.8 Kbaud communication with host computer
• Execution of code in RAM or FLASH
• FLASH security
• FLASH programming
13.4 Functional Description
Monitor ROM receives and executes commands from a host computer.
Figure 13-1 shows a sample 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
MC68HC908AS60 has a FLASH security feature to prevent external
viewing of the contents of FLASH. Proper procedures must be followed
to verify FLASH content. Access to the FLASH is denied to unauthorized
users of customer-specified software (see 13.4.7 Security).
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
MC68HC908AS60 — Rev. 1.0
Monitor ROM (MON)
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