MC68HC908GT16 Datasheet, PDF (215/412 Pages) Motorola, Inc – Microcontrollers

Monitor ROM (MON)
Functional Description
The computer operating properly (COP) module is disabled in monitor
mode based on these conditions:
• If monitor mode was entered as a result of the reset vector being
blank (above condition set 2 or 3), the COP is always disabled
regardless of the state of IRQ or RST.
• If monitor mode was entered with V_TST on IRQ (condition set 1),
then the COP is disabled as long as V_TST is applied to either IRQ
or RST.
The second condition states that as long as V_TST is maintained on the
IRQ pin after entering monitor mode, or if V_TST is applied to RST after
the initial reset to get into monitor mode (when V_TST was applied to IRQ),
then the COP will be disabled. In the latter situation, after V_TST is applied
to the RST pin, V_TST can be removed from the IRQ pin in the interest of
freeing the IRQ for normal functionality in monitor mode.
Figure 15-4 shows a simplified diagram of the monitor mode entry when
the reset vector is blank and just 1 x V_DD voltage is applied to the IRQ
pin. An external oscillator of 9.8304 MHz is required for a baud rate of
9600, as the internal bus frequency is automatically set to the external
frequency divided by four.
POR RESET
IS VECTOR
NO
BLANK?
YES
MONITOR MODE
EXECUTE
MONITOR
CODE
NORMAL USER
MODE
POR
NO
TRIGGERED?
YES
Figure 15-4. Low-Voltage Monitor Mode Entry Flowchart
MC68HC908GT16 • MC68HC908GT8 — Rev. 2
MOTOROLA
Monitor ROM (MON)
Technical Data
215