MC68HC908JK1 Datasheet, PDF (102/210 Pages) Motorola, Inc – MC68HC908JK1

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
• 960 bytes monitor ROM code size
• Monitor mode entry without high voltage, V_DD + V_HI, if reset vector
is blank ($FFFE and $FFFF contain $FF)
• Standard monitor mode entry if high voltage, V_DD + V_HI, is applied
to IRQ1
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 PTB0 pin. A
level-shifting and multiplexing interface is required between PTB0 and
the host computer. PTB0 is used in a wired-OR configuration and
requires a pull-up resistor.
Technical Data
102
1. No security feature is absolutely secure. However, Motorola’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.
Monitor ROM (MON)
MC68H(R)C908JL3 — Rev. 1.0
MOTOROLA