mc68hc908jb8 Freescale Semiconductor, Inc, mc68hc908jb8 Datasheet - Page 164

• Manufacturer Part Number: mc68hc908jb8
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Monitor ROM (MON)
10.3 Features
10.4 Functional Description
Technical Data
164
Features of the monitor ROM include the following:
The monitor ROM receives and executes commands from a host
computer.
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.
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.
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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 feature
FLASH memory programming interface
976 bytes monitor ROM code size
Monitor mode entry without high voltage, V
is blank ($FFFE and $FFFF contain $FF)
Standard monitor mode entry if high voltage, V
to IRQ
Figure 10-1
Monitor ROM (MON)
MC68HC908JB8•MC68HC08JB8•MC68HC08JT8 — Rev. 2.3
shows a example circuit used to enter monitor
1
DD
Freescale Semiconductor
+ V
DD
HI
+ V
, if reset vector
HI
, is applied