MC68HC908KX8 Datasheet, PDF (259/310 Pages) Motorola, Inc – Microcontrollers

Monitor ROM (MON)
Monitor Mode Vectors
NOTE:
In normal monitor mode with V_TST on IRQ1, the MCU alters
PTB7/(OSC2) to function as a RST pin. This is useful for testing the
MCU. Dropping IRQ1 voltage to below V_TST will revert PTB7/(OSC2) to
its user mode function.
The computer operating properly (COP) module is disabled in normal
monitor mode whenever V_TST is applied to the IRQ1 pin. If the voltage
on IRQ1 is less than V_TST, the COP module is controlled by the COPD
configuration bit.
18.5.2 Forced Monitor Mode
If the voltage applied to the IRQ1 is less than V_TST, the MCU will come
out of reset in user mode. The MENRST module is monitoring the reset
vector fetches and will assert an internal reset if it detects that the reset
vectors are erased ($FF). When the MCU comes out of reset, it is forced
into monitor mode without requiring high voltage on the IRQ1 pin.
Once out of reset, the monitor code is initially executing off the internal
clock at its default frequency. The monitor code reconfigures the ICG
module to use the external square-wave clock source. Switching to an
external clock source allows the MCU, using an appropriate clock
frequency, to communicate with host software at standard baud rates.
The COP module is disabled in forced monitor mode. Any reset other
than a power-on reset (POR) will automatically force the MCU to come
back to the forced monitor mode.
18.6 Monitor Mode Vectors
Monitor mode uses alternate vectors for reset and SWI interrupts. The
alternate vectors are in the $FE page instead of the $FF page and allow
code execution from the internal monitor firmware instead of user code.
MC68HC908KX8 • MC68HC908KX2 • MC68HC08KX8 — Rev. 1.0
MOTOROLA
Monitor ROM (MON)
Technical Data
259