MC68HC908GT16_07 Datasheet, PDF (248/292 Pages) Freescale Semiconductor, Inc – Microcontrollers

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If monitor mode was entered with V_TST on IRQ, then the COP is disabled as long as V_TST is applied to
either IRQ or RST.
This 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.
19.3.1.2 Forced Monitor Mode
If entering monitor mode without high voltage on IRQ (where applied voltage is either V_DD or V_SS), then
all port C pin requirements and conditions, including the PTC3 frequency divisor selection, are not in
effect. This is to reduce circuit requirements when performing in-circuit programming.
If IRQ = V_DD on monitor mode entry, an external oscillator of 9.8304 MHz is required for a 9600 baud rate.
If IRQ = V_SS on monitor mode entry, the ICG generates a 9600 baud rate using the trimmed ICG value in
the ICGTR5 register. If the ICGTR5 register is blank, the baud rate will be a nominal 9600 baud which
may not be adequate for standard PC serial communication.
When forced monitor mode is entered, the COP is always disabled regardless of the state of IRQ or RST.
NOTE
If the reset vector is blank and monitor mode is entered, the chip will see an
additional reset cycle after the initial POR reset. Once the part has been
programmed, the traditional method of applying a voltage, V_TST, to IRQ
must be used to enter monitor mode.
19.3.1.3 Monitor Vectors
In monitor mode, the MCU uses different vectors for reset, SWI (software interrupt), and break interrupt
than those for user mode. 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.
NOTE
Exiting monitor mode after it has been initiated by having a blank reset
vector requires a power-on reset (POR). Pulling RST low will not exit
monitor mode in this situation.
Table 19-2 summarizes the differences between user mode and monitor mode.
Table 19-2. Mode Differences
Modes
User
Monitor
Reset
Vector High
$FFFE
$FEFE
Reset
Vector Low
$FFFF
$FEFF
Functions
Break
Break
Vector High Vector Low
$FFFC
$FFFD
$FEFC
$FEFD
SWI
Vector High
$FFFC
$FEFC
SWI
Vector Low
$FFFD
$FEFD
MC68HC908GT16 • MC68HC908GT8 • MC68HC08GT16 Data Sheet, Rev. 5.0
248
Freescale Semiconductor