MC908AB32CFUE Datasheet, PDF (158/392 Pages) Freescale Semiconductor, Inc – Microcontrollers

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
• FLASH memory security feature¹
• Execution of code in RAM or FLASH
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 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.
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
158
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.
Monitor ROM (MON)
MC68HC908AB32 — Rev. 1.1
Freescale Semiconductor