4524_M Datasheet, PDF (251/310 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 720 FAMILY / 4500 SERIES

4524 Group
APPLICATION
2.10 Oscillation circuit
2.10 Oscillation circuit
The 4524 Group has an internal oscillation circuit to produce the clock required for microcomputer operation.
The ceramic resonator or the RC oscillation can be used for the main clock (f(XIN)).
After system is released from reset, the 4524 Group starts operation by the clock output from the on-chip
oscillator which is the internal oscillator.
2.10.1 Oscillation circuit
(1) Main clock generating circuit (f(XIN))
The ceramic resonator or RC oscillation can
be used for the main clock (f(XIN)).
After system is released from reset, the 4524
Group starts operation by the clock output from
the on-chip oscillator which is the internal
oscillator.
When the ceramic resonator is used, execute
the CMCK instruction. When the RC oscillation
is used, execute the CRCK instruction. The
selection of oscillation circuit by the CMCK or
CRCK instruction is valid only at once. The
oscillation circuit corresponding to the first
executed one of these two instructions is valid.
Another oscillation circuit and the on-chip
oscillator stop.
Execute the CMCK or the CRCK instruction
in the initial setting routine 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,
the 4524 Group operates by the on-chip
oscillator.
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. 2.10.1 Switch to ceramic oscillation/RC oscillation
M34524
XIN
XOUT
* Do not use the CMCK instruction
and CRCK instruction in program.
Fig. 2.10.2 Handling of XIN and XOUT when operating
on-chip oscillator
(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
oscillation, connect XIN pin to VSS and leave
XOUT pin open (Figure 2.10.2).
The clock frequency of the on-chip oscillator
depends on the supply voltage and the
operation temperature range.
Be careful that margin of frequencies when
designing application products.
Rev.2.00 Aug, 06 2004
REJ09B0107-0200Z
2-87