MC908JB16DWE Datasheet, PDF (124/332 Pages) Freescale Semiconductor, Inc – Microcontrollers

Monitor ROM (MON)
9.3 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
• Execution of code in RAM or FLASH
• FLASH memory security feature¹
• FLASH memory programming interface
• 1,472 bytes monitor ROM code size
• Monitor mode entry without high voltage, V_TST, if reset vector is
blank ($FFFE and $FFFF contain $FF)
• Standard monitor mode entry if high voltage, V_TST, is applied to
IRQ
9.4 Functional Description
The monitor ROM receives and executes commands from a host
computer. Figure 9-1 shows a example circuit used to enter monitor
mode and communicate with a host computer via a standard RS-232
interface.
Simple monitor commands can access any memory address. In monitor
mode, the MCU can execute host-computer code in RAM while most
MCU pins 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.
Technical Data
124
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)
MC68HC908JB16 — Rev. 1.1
Freescale Semiconductor