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APPLICATION
2-49
4501 Group User’s Manual
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 ring
oscillator which is the internal oscillator.
Fig. 2.8.1 Switch to ceramic resonance/RC oscillation
Reset
Ring oscillator
operation
CMCK instruction
CRCK instruction
Ceramic resonator valid
Ring oscillator stop
RC oscillation stop
RC oscillation valid
Ring oscillator stop
Ceramic resonator stop
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 ring 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 ring 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 ring oscillator.
(2)
Ring oscillator operation
When the MCU operates by the ring 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 ring oscillator
depends on the supply voltage and the
operation temperature range.
Be careful that variable frequencies when
designing application products.
Fig. 2.8.2 Handling of XIN and XOUT when operating
ring oscillator
4501
XIN
XOUT
*
Do not use the CMCK instruction
and CRCK instruction in program.