4509 Datasheet, PDF (57/142 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

4509 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 oscilla-
tor.
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))
The ceramic resonator or RC oscillation can be used for the main
clock of this product.
After system is released from reset, the ceramic oscillation is active
for main clock.
The ceramic oscillation is invalid and the RC oscillation circuit is
valid with the CRCK instruction.
Execute the CRCK instruction in the initial setting routine of program
(executing it in address 0 in page 0 is recommended).
The execution of the CRCK instruction can be valid only once.
Register MR controls the enable/disable of the oscillation and the
selection of the operation source clock.
Also, when the MCU operates only by the on-chip oscillator without
using main clock f(XIN), connect XIN pin to Vss and leave XOUT pin
open, and do not execute the CRCK instruction (Figure 51).
(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 between
pins XIN and XOUT (Figure 52).
Do not execute the CRCK instruction.
Set “0” to bit 0 of register MR after the oscillation stabilizing wait
time is generated by software to select the clock generated by the
ceramic oscillation circuit for the source oscillation clock.
(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 53).
The frequency is affected by a capacitor, a resistor and a microcom-
puter. So, set the constants within the recommended operating
condition of the frequency limits.
Reset
Main clock f(XIN)
• Ceramic oscillation valid
• RC oscillation invalid
CRCK instruction
• Ceramic oscillation invalid
• RC oscillation valid
Fig. 50 Switch to ceramic oscillation/RC oscillation
4509
* Do not execute the CRCK
instruction in program.
XIN
XOUT
Fig. 51 Handling of XIN and XOUT when main clock is not used
XIN
CIN
4509
* Do not execute the CRCK
instruction 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. 52 Ceramic resonator external circuit
4509
* Execute the CRCK
instruction in program.
R
XIN
XOUT
C
Fig. 53 External RC circuit
Rev.1.02 2006.12.22 page 57 of 140
REJ03B0147-0102