4501_M Datasheet, PDF (166/212 Pages) Renesas Technology Corp – 4-BIT CISC SINGLE-CHIP MICROCOMPUTER 4500 SERIES

4501 Group
APPLICATION
2.8 Oscillation circuit
2.8 Oscillation circuit
The 4501 Group has an internal oscillation circuit to produce the clock required for microcomputer operation.
The ceramic resonance and the RC oscillation can be used for the source clock.
After system is released from reset, the 4501 Group starts operation by the clock output from the on-chip
oscillator which is the internal oscillator.
2.8.1 Oscillation circuit
(1) f(XIN) clock generating circuit
The ceramic resonator or RC oscillation can
be used for the source oscillation (f(XIN)) of
the MCU.
After system is released from reset, the 4501
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
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 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 4501 Group operates by the on-chip
oscillator.
(2) On-chip oscillator operation
When the MCU operates by the on-chip
oscillator as the source oscillation (f(XIN))
without using the ceramic resonator or the
RC oscillator, connect XIN pin to VSS and leave
XOUT pin open (Figure 2.8.2).
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.
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. 2.8.1 Switch to ceramic resonance/RC oscillation
4501
* Do not use the CMCK instruction
and CRCK instruction in program.
XIN
XOUT
Fig. 2.8.2 Handling of XIN and XOUT when operating
on-chip oscillator
Rev.2.01 Feb 07, 2005
REJ09B0192-0201
2-49