455A Datasheet, PDF (63/148 Pages) Renesas Technology Corp – SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER

455A Group
(1) High-speed on-chip oscillator operation
After system is released from reset, the MCU starts operation by
the clock output from the high-speed on-chip oscillator which is
the internal oscillator.
The clock frequency of the high-speed on-chip oscillator depends
on the supply voltage and the operation temperature range.
Be careful that variable frequencies when designing application
products.
455A
XIN
XOUT
(2) Main clock generating circuit (f(XIN))
After reset release, the ceramic oscillation is valid for the main
clock. Connect the ceramic oscillator and the external circuit to
pins XIN and XOUT at the shortest distance (Figure 61). A
feedback resistor is built in between pins XIN and XOUT.
If the main clock is not used, connect the XIN pin to VSS and
leave the XOUT pin open.
(3) Low-speed on-chip oscillator operation
After system is released from reset, the low-speed on-chip
oscillator turns invalid which is the internal oscillator.
Oscillator operation/stopping and the control of system clock
selection are operated by the register RG and MR.
The clock frequency of the low-speed on-chip oscillator depends
on the supply voltage and the operation temperature range.
Be careful that variable frequencies when designing application
products.
Fig 60. Handling of XIN and XOUT when operating on-
chip oscillator
455A
XIN
XOUT
Rd
CIN
COUT
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 61. Ceramic resonator external circuit
Rev.1.01 Feb 15, 2008 Page 63 of 146
REJ03B0224-0101