Monitor ROM (MON)
10.2 Introduction
This section describes the monitor ROM (MON) and the monitor mode
entry methods. The monitor ROM allows complete testing of the MCU
through a single-wire interface with a host computer. Monitor mode entry
can be achieved without use of the higher test voltage, V
, as long as
TST
vector addresses $FFFE and $FFFF are blank, thus reducing the
hardware requirements for in-circuit programming.
In addition, to simply user coding, routines are also stored in the monitor
ROM area for FLASH memory program /erase and EEPROM emulation.
10.3 Features
Features of the monitor ROM include:
•
•
Normal user-mode pin functionality
One pin dedicated to serial communication between monitor ROM
and host computer
•
Standard mark/space non-return-to-zero (NRZ) communication
with host computer
•
•
•
•
Execution of code in RAM or FLASH
1
FLASH memory security feature
FLASH memory programming interface
Enhanced PLL (phase-locked loop) option to allow use of external
32.768-kHz crystal to generate internal frequency of 2.4576 MHz
•
•
•
•
960 bytes monitor ROM code size
($FC00–$FDFF and $FE10–$FFCE)
Monitor mode entry without high voltage, V
blank ($FFFE and $FFFF contain $FF)
, if reset vector is
TST
Standard monitor mode entry if high voltage, V
IRQ
, is applied to
TST
Resident routines for in-circuit programming and EEPROM
emulation
1. No security feature is absolutely secure. However, Freescale’s strategy is to make reading or
copying the FLASH difficult for unauthorized users.
Technical Data
156
MC68HC908LJ12 — Rev. 2.1
Monitor ROM (MON)
Freescale Semiconductor
FREESCALE [ Freescale ]
