mc68hc908gp20 Freescale Semiconductor, Inc, mc68hc908gp20 Datasheet - Page 208

• Manufacturer Part Number: mc68hc908gp20
• Description: M68hc08 Family Of 8-bit Microcontroller Units Mcus
• Manufacturer: Freescale Semiconductor, Inc

15.4.1 Entering Monitor Mode
Advance Information
208
between PTA0 and the host computer. PTA0 is used in a wired-OR
configuration and requires a pullup resistor.
The monitor code has been updated from previous versions of the
monitor code to allow enabling the PLL to generate the internal clock,
provided the reset vector is blank, when the device is being clocked by
a low-frequency crystal. This addition, which is enabled when IRQ is
held low out of rest, is intended to support serial communication/
programming at 9600 baud in monitor mode by stepping up the external
frequency (assumed to be 32.768 kHz) by a fixed amount to generate
the desired internal frequency (2.4576 MHz). Since this feature is
enabled only when IRQ is held low out of reset, it cannot be used when
the reset vector is non-zero because entry into monitor mode in this case
requires V
Table 15-1
specified in the table, monitor mode may be entered after a POR and will
allow communication at 9600 baud provided one of the following sets of
conditions is met:
If V
(above condition set 1), the bus frequency is a divide-by-two of the input
clock. If PTC3 is high with V
the bus frequency will be a divide-by-four of the input clock. Holding the
1. If $FFFE and $FFFF contain non-zero values:
2. If $FFFE and $FFFF contain zero values:
3. If $FFFE and $FFFF contain zero values:
TST
– The external clock is 4.9152 MHz with PTC3 low or
– IRQ = V
– The external clock is 9.8304 MHz
– IRQ = V
– The external clock is 32.768 kHz (crystal)
– IRQ = V
is applied to IRQ and PTC3 is low upon monitor mode entry
9.8304 MHz with PTC3 high
pullup; PLL off)
32.768 kHz to an internal bus frequency of 2.4576 MHz)
TST
shows the pin conditions for entering monitor mode. As
on IRQ.
DD
TST
SS
(this setting initiates the PLL to boost the external
(this can be implemented through the internal IRQ
(PLL off)
TST
applied to IRQ upon monitor mode entry,
MC68HC908GP20
Freescale Semiconductor
—
Rev 2.1