MOTOROLA
MC68341 USER’S MANUAL
2- 11
2.6 CLOCK SIGNALS
These signals are used by the MC68341 for controlling or generating the system clocks.
See Section 4 System Integration Module for more information on the various clocking
methods and frequencies.
2.6.1 System Clock (CLKOUT)
This output signal is the system clock output and is used as the bus timing reference by
external devices. CLKOUT can be varied in frequency or slowed in low power stop mode
to conserve power.
2.6.2 Crystal Oscillator (EXTAL, XTAL)
These two pins are the connections for an external crystal to the internal oscillator circuit.
2.6.3 External Clock (EXTCLK)
This pin used to connect an external clcok source. This input is divided by two until the V-
bit in the SYNCR is set.
2.6.4 External Filter Capacitor (XFC)
This pin is used to add an external capacitor to the filter circuit of the phase-locked loop.
The capacitor should be connected between XFC and VCCSYN.
2.6.5 Clock Mode Select (MODCK, Port B0)
This pin selects the source of the internal system clock during reset. After reset, it can be
programmed to be port B parallel I/O.
MODCK
The state of this active-high input signal during reset selects the source of the internal
system clock. If MODCK is high during reset, the internal voltage-controlled oscillator
(VCO) furnishes the system clock in crystal mode. If MODCK is low during reset, an
external clock source at the EXTCLK pin furnishes the system clock output in external
clock mode.
Port B0
This pin can be used as a port B parallel I/O.
2.7 INSTRUMENTATION AND EMULATION SIGNALS
These signals are used for test or software debugging. See Section 5 CPU32 for more
information on these signals and background debug mode.
2.7.1 Instruction Fetch
(IFETCH / DSI)
This pin functions as IFETCH in normal operation and as DSI in background debug mode .
F
re
e
sc
a
le
S
e
m
ic
o
n
d
u
c
to
r,
I
Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
n
c
..
.