Datasheet

MC68HC908QY4•MC68HC908QT4•MC68HC908QY2•MC68HC908QT2•MC68HC908QY1•MC68HC908QT1
114 Monitor ROM (MON) MOTOROLA
Monitor ROM (MON)
NON-DISCLOSURE AGREEMENT REQUIRED
9.3 Features
Features of the monitor ROM include:
• Normal user-mode pin functionality on most pins
• One pin dedicated to serial communication between monitor
read-only memory (ROM) and host computer
• Standard mark/space non-return-to-zero (NRZ) communication
with host computer
• Execution of code in random-access memory (RAM) or FLASH
• FLASH memory security feature
(1)
• FLASH memory programming interface
• Use of external 9.83 MHz crystal or clock to generate internal
frequency of 2.4576 MHz
• Simple internal oscillator mode of operation (no external clock or
high voltage)
• 574 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 is applied to IRQ
9.4 Functional Description
The monitor ROM receives and executes commands from a host
computer. Figure 9-1, Figure 9-2, and Figure 9-3 show example circuits
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 code downloaded into RAM by a host
computer while most MCU pins retain normal operating mode functions.
All communication between the host computer and the MCU is through
1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.