4559 Datasheet, PDF (62/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4559 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
oscillator.
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
oscillator 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
(executing 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 61).
Reset
Main clock (f(XIN))
• Ceramic resonator circuit valid
• RC oscillation circuit invalid
CRCK
• Ceramic resonator circuit invalid
• RC oscillation circuit valid
Fig 60. Switch to ceramic resonance/RC oscillation
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XIN
XOUT
(3) Ceramic resonator
When the ceramic resonator is used as the main clock (f(XIN)),
connect the ceramic resonator and the external circuit to pins XIN
and XOUT at the shortest distance.
A feedback resistor is built in between pins XIN and XOUT
(Figure 62). 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 63).
To select RC oscillation as the system clock, select the main
clock (f(XIN) as the system clock by bits 0 and 1 of the clock
control register MR.
The frequency is affected by a capacitor, a resistor and a
microcomputer. So, set the constants within the range of the
frequency limits.
* ^{Do not use the CRCK instruction in program.}
Fig 61. Handling of XIN and XOUT when operating on-
chip oscillator
4559
XIN
XOUT
Rd
CIN
COUT
Rev.1.04 Aug 23, 2007 Page 62 of 146
REJ03B0188-0104
* ^{Do not execute the CRCK instruction in program.}
Note: Externally connect a damping resistor Rd
depending on the oscillation frequency.
(A feedback resistor is built-in.)
Use the resonator manufacturer’s recommended
value because constants such as capacitance
depend on the resonator.
Fig 62. Ceramic resonator external circuit
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R
XIN
XOUT
C
* Execute the CRCK
instruction in program.
Fig 63. External RC oscillation circuit