MC68HC908LJ24 Datasheet, PDF(167/464 Page) Motorola, Inc – Microcontrollers

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MC68HC908LJ24 Datasheet, PDF (167/464 Pages) Motorola, Inc – Microcontrollers

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Freescale Semiconductor, Inc.

Monitor ROM (MON)

Functional Description

10.4.1 Entering Monitor Mode

Table 10-1 shows the pin conditions for entering monitor mode. As

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:

1. If $FFFE and $FFFF do not contain $FF (programmed state):

â The external clock is 4.9152 MHz with PTC1 low or

9.8304 MHz with PTC1 high

â IRQ = VTST (PLL off)

2. If $FFFE and $FFFF both contain $FF (erased state):

â The external clock is 9.8304 MHz

â IRQ = VDD (this can be implemented through the internal IRQ

pullup; PLL off)

3. If $FFFE and $FFFF both contain $FF (erased state):

â The external clock is 32.768 kHz (crystal)

â IRQ = VSS (this setting initiates the PLL to boost the external

32.768 kHz to an internal bus frequency of 2.4576 MHz)

If VTST is applied to IRQ and PTC1 is low upon monitor mode entry

(above condition set 1), the bus frequency is a divide-by-two of the input

clock. If PTC1 is high with VTST applied to IRQ upon monitor mode entry,

the bus frequency will be a divide-by-four of the input clock. Holding the

PTC1 pin low when entering monitor mode causes a bypass of a divide-

by-two stage at the oscillator only if VTST is applied to IRQ. In this event,

the CGMOUT frequency is equal to the CGMXCLK frequency, and the

OSC1 input directly generates internal bus clocks. In this case, the

OSC1 signal must have a 50% duty cycle at maximum bus frequency.

If entering monitor mode without high voltage on IRQ (above condition

set 2 or 3, where applied voltage is either VDD or VSS), then all port A pin

requirements and conditions, including the PTC1 frequency divisor

selection, are not in effect. This is to reduce circuit requirements when

performing in-circuit programming.

MC68HC908LJ24/LK24 â Rev. 2

MOTOROLA

Monitor ROM (MON)

For More Information On This Product,

Go to: www.freescale.com

Data Sheet

167

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