MC68HC08AZ16 Datasheet, PDF (139/527 Pages) Motorola, Inc – HCMOS Microcontroller Unit

Monitor ROM (MON)
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-28.8K baud communication with host computer
• Execution of code in RAM or ROM
• EEPROM programming
• ROM security
Functional description
The monitor ROM receives and executes commands from a host
computer. Figure 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
MC68HC08AZ32 has a ROM security feature to prevent extrnal viewing
of the contents of ROM. Proper procedures must be followed to verify
ROM content. Access to the ROM is denied to unauthorized users of
customer specified software. See Security on page 146.
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 pull-up resistor.
MC68HC08AZ32
138
Monitor ROM (MON)
2--mon
MOTOROLA