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MC68HC908JB8 Datasheet, PDF (164/286 Pages) Motorola, Inc – MICROCONTROLLERS | |||
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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
⢠Execution of code in RAM or FLASH
⢠FLASH memory security feature1
⢠FLASH memory programming interface
⢠976 bytes monitor ROM code size
⢠Monitor mode entry without high voltage, VDD + VHI, if reset vector
is blank ($FFFE and $FFFF contain $FF)
⢠Standard monitor mode entry if high voltage, VDD + VHI, is applied
to IRQ
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.
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
164
1. No security feature is absolutely secure. However, Freescaleâs strategy is to make reading or
copying the FLASH difficult for unauthorized users.
MC68HC908JB8â¢MC68HC08JB8â¢MC68HC08JT8 â Rev. 2.3
Monitor ROM (MON)
Freescale Semiconductor
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