4554 Datasheet, PDF (61/138 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4554 Group
(1) Main clock generating circuit (f(XIN))
The ceramic resonator or RC oscillation can be used for the main
clock of this MCU.
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.
When the ceramic resonator is used, execute the CMCK instruc-
tion. When the RC oscillation is used, execute the CRCK
instruction. The oscillation circuit by the CMCK or CRCK instruction
can be selected only at once. The oscillation circuit corresponding
to the first executed one of these two instructions is valid. Other os-
cillation circuit and the on-chip oscillator stop.
Execute the CMCK or the CRCK instruction in the initial setting rou-
tine of program (executing it in address 0 in page 0 is
recommended). Also, when the CMCK or the CRCK instruction is
not executed in program, this MCU operates by the on-chip oscilla-
tor.
(2) On-chip oscillator operation
When the MCU operates by the on-chip oscillator as the main clock
(f(XIN)) without using the ceramic resonator or the RC oscillator,
connect XIN pin to VSS and leave XOUT pin open (Figure 49).
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.
(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. Then, execute the CMCK instruction.
A feedback resistor is built in between pins XIN and XOUT (Figure
50).
(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
On-chip oscillator
operation
CMCK instruction
CRCK instruction
• Ceramic resonator valid • RC oscillation valid
• On-chip oscillator stop • On-chip oscillator stop
• RC oscillation stop
• Ceramic resonator stop
Fig. 48 Switch to ceramic resonance/RC oscillation
M34554
XIN
XOUT
* Do not use the CMCK instruction
and CRCK instruction in program.
Fig. 49 Handling of XIN and XOUT when operating on-chip oscillator
XIN
CIN
M34554
* Execute the CMCK instruc-
tion 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
M34554
* ^{Execute the CRCK}
R
XIN
XOUT
instruction in program.
C
Fig. 51 External RC oscillation circuit
Rev.3.00 Aug 06, 2004 page 61 of 136
REJ03B0043-0300Z