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Functional Description
MC68HC908JL8/JK8 MC68HC08JL8/JK8 MC68HC908KL8 Data Sheet, Rev. 3.1
Freescale Semiconductor
87
7.3.1 Entering Monitor Mode
Table 7-1 shows the pin conditions for entering monitor mode. As specified in the table, monitor mode
may be entered after a POR.
Communication at 9600 baud will be established provided one of the following sets of conditions is met:
1.
If IRQ = VTST:
–
Clock on OSC1 is 4.9125MHz
–PTB3 = low
2.
If IRQ = VTST:
–
Clock on OSC1 is 9.8304MHz
–
PTB3 = high
3.
If $FFFE and $FFFF are blank (contain $FF):
–
Clock on OSC1 is 9.8304MHz
–IRQ = VDD
If VTST is applied to IRQ and PTB3 is low upon monitor mode entry (Table 7-1 condition set 1), the bus frequency is a divide-by-two of the clock input to OSC1. If PTB3 is high with VTST applied to IRQ upon
monitor mode entry (
Table 7-1 condition set 2), the bus frequency is a divide-by-four of the clock input to
OSC1. Holding the PTB3 pin low when entering monitor mode causes a bypass of a divide-by-two stage
at the oscillator only if VTST is applied to IRQ. In this event, the OSCOUT frequency is equal to the
2OSCOUT frequency, and OSC1 input directly generates internal bus clocks. In this case, the OSC1
signal must have a 50% duty cycle at maximum bus frequency.
Entering monitor mode with VTST on IRQ, the COP is disabled as long as VTST is applied to either IRQ or
If entering monitor mode without high voltage on IRQ and reset vector being blank ($FFFE and $FFFF)
(Table 7-1 condition set 3, where applied voltage is VDD), then all port B pin requirements and conditions, Table 7-1. Monitor Mode Entry Requirements and Options
IRQ
$FFFE
and
$FFFF
PTB3
PTB2
PTB1
PTB0
OSC1 Clock(1)
1. RC oscillator cannot be used for monitor mode; must use either external oscillator or XTAL oscillator circuit.
Bus Frequency
Comments
VTST
(2)
2. See Table 17-4 for VTST voltage level requirements. X
0011
4.9152MHz
2.4576MHz
High voltage entry to monitor
mode.
9600 baud communication on
PTB0. COP disabled.
VTST
(1)
X
1011
9.8304MHz
2.4576MHz
VDD
BLANK
(contain
$FF)
X
1
9.8304MHz
2.4576MHz
Blank reset vector
(low-voltage) entry to monitor
mode.
9600 baud communication on
PTB0. COP disabled.
VDD
NOT
BLANK
XXXX
X
OSC1 ÷ 4
Enters User mode.