7480 Datasheet, PDF (43/98 Pages) Bi technologies – 7/8 Diameter 5-Turn Wirewound Precision Potentiometer

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MITSUBISHI MICROCOMPUTERS
7480/7481 GROUP
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
Clock Generating Circuit
The 7480/7481 group is provided with a built-in oscillation circuit.
An oscillation circuit can be formed by connecting a resonator be-
tween XIN and XOUT. Use the manufacturer's recommended
values for constants such as capacitance, which will differ de-
pending on each resonator. The 7480/7481 group has a built-in
feedback resistor between the XIN and XOUT pins, so an external
resistor can be omitted.
q Frequency Control
(1) High-speed Mode
The frequency applied to the clock input pin XIN divided by 2 is
used as the internal clock φ. This mode is set after reset release.
(2) Medium-speed Mode
The frequency applied to the clock input pin XIN divided by 8 is
used as the internal clock φ.
q Oscillation Frequency
(1) Stop Mode
If the STP instruction is executed, the internal clock φ stops at an
“H” level, and the oscillator stops. At this time, timer 1 is set to
“FF16,” and f(XIN)/8 is forcibly connected to the count source of
timer 1. Accordingly, set the timer 1 interrupt enable bit to the dis-
able status (“0”) before execution of the STP instruction.
When a reset or an external interrupt is accepted, oscillation is re-
started, but the internal clock φ is supplied to the CPU after timer
1 underflows. This is because when an external resonator is used,
some time is required until a start of oscillation.
(2) Wait Mode
If the WIT instruction is executed, the internal clock φ stops at an
“H” level. But, the oscillator does not stop. When a reset or inter-
rupt is accepted, the stop status is released. The microcomputer
can execute any instruction immediately, because the oscillator
does not stop.
XIN
XOUT
Rd
CIN
COUT
Fig. 44 External circuit of ceramic resonator
XIN
XOUT
Open
External oscillation
circuit
VCC
VSS
Duty ratio 50%
Fig. 45 External clock input circuit
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