Rev.2.00
Aug 28, 2006
page 60 of 119
7643 Group
REJ03B0054-0200
CLOCK GENERATING CIRCUIT
The 7643 group has two built-in oscillation circuits. An oscillation
circuit can be formed by connecting a resonator between XIN and
XOUT (XCIN and XCOUT). Use the circuit constants in accordance
with the resonator manufacturer’s recommended values. No exter-
nal resistor is needed between XIN and XOUT since a feed-back
resistor exists on-chip. (An external feed-back resistor may be
needed depending on conditions.) However, an external feed-back
resistor is needed between XCIN and XCOUT.
When using an external clock, input the clocks to the XIN or XCIN
pin and leave the XOUT or XCOUT pin open.
Immediately after power on, only the XIN oscillation circuit starts
oscillating, and XCIN and XCOUT pins function as I/O ports.
Frequency Control
The internal system clock can be selected among fSYN, f(XIN),
f(XIN)/2, and f(XCIN). The internal clock
φ is half the frequency of
internal system clock.
(1) fSYN clock
This is made by the frequency synthesizer. f(XIN) or f(XCIN) can be
selected as its input clock. See also section “FREQUENCY SYN-
THESIZER”.
(2) f(XIN) clock
The frequency of internal system clock is the frequency of XIN pin.
(3) f(XIN)/2 clock
The frequency of internal system clock is half the frequency of XIN
pin.
(4) f(XCIN) clock
The frequency of internal system clock is the frequency of XCIN
pin.
sNote
If you switch the oscillation between XIN - XOUT and XCIN - XCOUT,
stabilize both XIN and XCIN oscillations. The sufficient time is re-
quired for the XCIN oscillation to stabilize, especially immediately
after power on and at returning from the stop mode.
Fig. 56 Ceramic resonator or quartz-crystal oscillator exter-
nal circuit
Fig. 57 External clock input circuit
XCIN
XCOUT
XIN
XOUT
CIN
COUT
CCIN
CCOUT
Rf
Rd
Notes : Insert a damping resistor if required. The
resistance will vary depending on the oscillator and
the oscillation drive capacity setting. Use the value
recommended by the maker of the oscillator. Also,
if the oscillator manufacturer's data sheet specifies
that a feedback resistor be added external to the
chip though a feedback resistor exists on-chip,
insert a feedback resistor between XIN and XOUT
following the instruction.
Rd (Note)
VCC
VSS
XCIN
XCOUT
XIN
XOUT
Open
External oscillation
circuit
External oscillation
circuit
VCC
VSS