MC68HC08AS32 Datasheet, PDF (255/280 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

16.3 Monitor ROM (MON)
The monitor ROM allows complete testing of the MCU through a single-wire
interface with a host computer.
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 ROM
16.3.1 Functional Description
Monitor ROM receives and executes commands from a host computer.
Figure 16-6 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
MC68HC08AS32 has a ROM security feature that requires proper procedures to
be followed before the ROM can be accessed. 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.
MC68HC08AS32 — Rev. 4.1
Freescale Semiconductor
Data Sheet
255