4552 Datasheet, PDF (58/145 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4552 Group
(1) On-chip oscillator operation
After system is released from reset, the MCU starts operation by
the clock output from the on-chip oscillator which is the internal os-
cillator.
The clock frequency of the on-chip oscillator depends on the supply
voltage and the operation temperature range.
Be careful that variable frequencies when designing application
products.
(2) Main clock generating circuit (f(XIN))
When the MCU operates by the ceramic resonator or the RC oscil-
lator as the main clock (f(XIN)).
After system is released from reset, the ceramic oscillation is valid
for main clock.
The ceramic oscillation is invalid and the RC oscillation circuit is
valid with the CRCK instruction.
The CRCK instruction can be executed only once.
Execute the CRCK instruction in the initial setting routine (execut-
ing it in address 0 in page 0 is recommended).
When the main clock (f(XIN)) is not used, connect XIN pin to VSS
and leave XOUT pin open, and do not execute the CRCK instruction
(Figure 49).
(3) Ceramic resonator
When the ceramic resonator is used as the main clock (f(XIN)), con-
nect 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 (Figure 50). Do not execute the CRCK
instruction in program.
(4) RC oscillation
When the RC oscillation is used as the main clock (f(XIN)), connect
the XIN pin to the external circuit of resistor R and the capacitor C
at the shortest distance and leave XOUT pin open. Then, execute
the CRCK instruction (Figure 51).
The frequency is affected by a capacitor, a resistor and a micro-
computer. So, set the constants within the range of the frequency
limits.
Reset
Main clock (f(XIN))
• Ceramic oscillation circuit valid
• RC oscillation circuit invalid
CRCK
• Ceramic oscillation circuit invalid
• RC oscillation circuit valid
Fig. 48 Switch to ceramic oscillation/RC oscillation
M34552
XIN
XOUT
* Do not use the CRCK instruction in
program.
Fig. 49 Handling of XIN and XOUT when operating on-chip oscillator
XIN
CIN
M34552
* Do not execute the CRCK in-
struction in program.
XOUT
Note: Externally connect a damping
resistor Rd depending on the
Rd
oscillation frequency.
(A feedback resistor is built-in.)
Use the resonator manu-
COUT
facturer’s recommended value
because constants such as ca-
pacitance depend on the
resonator.
Fig. 50 Ceramic resonator external circuit
M34552
* Execute the CRCK
instruction in program.
R
XIN
XOUT
C
Fig. 51 External RC circuit
Rev.3.02 Dec 22, 2006 page 58 of 142
REJ03B0023-0302