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HARDWARE
7540 Group User’s Manual
1-45
Fig. 46 External circuit of ceramic resonator
Fig. 47 External circuit of RC oscillation
XIN
COUT
CIN
XOUT
M37540
Rd
XIN
XOUT
C
R
M37540
Fig. 48 External clock input circuit
XIN
XOUT
External oscillation
circuit
VCC
VSS
Open
M37540
XIN
XOUT
M37540
Open
Fig. 49 Processing of XIN and XOUT pins at ring oscillator op-
eration
Clock Generating Circuit
An oscillation circuit can be formed by connecting a resonator be-
tween XIN and XOUT, and an RC oscillation circuit can be formed
by connecting a resistor and a capacitor.
Use the circuit constants in accordance with the resonator
manufacturer's recommended values.
(1) Ring oscillator operation
When the MCU operates by the ring oscillator for the main clock,
connect XIN pin to VSS and leave XOUT pin open.
The clock frequency of the ring oscillator depends on the supply
voltage and the operation temperature range.
Be careful that variable frequencies when designing application
products.
(2) Ceramic resonator
When the ceramic resonator is used for the main clock, connect
the ceramic resonator and the external circuit to pins XIN and
XOUT at the shortest distance. A feedback resistor is built in be-
tween pins XIN and XOUT.
(3) RC oscillation
When the RC oscillation is used for the main clock, connect the
XIN pin to the external circuit of resistor R and the capacitor C at
the shortest distance and leave XOUT pin open.
The frequency is affected by a capacitor, a resistor and a micro-
computer.
So, set the constants within the range of the frequency limits.
(4) External clock
When the external signal clock is used for the main clock, connect
the XIN pin to the clock source and leave XOUT pin open.
Select “ceramic resonance” by setting “0” to the Oscillation mode
selection bit of CPU mode register (address 003B16).
Externally connect a
damping resistor Rd de-
pending
on
the
oscillation frequency.
(A feedback resistor is
built-in.)
Use
the
resonator
manufacturer’s recom-
mended value because
constants such as ca-
pacitance depend on the
resonator.
Note:
Connect the external
circuit of resistor R
and the capacitor C at
the shortest distance.
The frequency is af-
fected by a capacitor,
a resistor and a micro-
computer.
So, set the constants
within the range of the
frequency limits.
Note:
The clock frequency of the
ring oscillator depends on
the supply voltage and the
operation temperature
range.
Be careful that variable fre-
quencies and obtain the
sufficient margin.
Note:
FUNCTIONAL DESCRIPTION