M38503MXH Datasheet, PDF (35/86 Pages) Mitsubishi Electric Semiconductor – SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS
3850 Group (Spec. H)
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
CLOCK GENERATING CIRCUIT
The 3850 group (spec. H) has two built-in oscillation circuits. An
oscillation circuit can be formed by connecting a resonator be-
tween XIN and XOUT (XCIN and XCOUT). Use the circuit constants
in accordance with the resonator manufacturer ’s recommended
values. No external resistor is needed between XIN and XOUT
since a feed-back resistor exists on-chip. However, an external
feed-back resistor is needed between XCIN and XCOUT.
Immediately after power on, only the XIN oscillation circuit starts
oscillating, and XCIN and XCOUT pins function as I/O ports.
Frequency Control
(1) Middle-speed mode
The internal clock φ is the frequency of XIN divided by 8. After re-
set, this mode is selected.
(2) High-speed mode
The internal clock φ is half the frequency of XIN.
(3) Low-speed mode
The internal clock φ is half the frequency of XCIN.
sNote
If you switch the mode between middle/high-speed and low-
speed, stabilize both XIN and XCIN oscillations. The sufficient time
is required for the sub-clock to stabilize, especially immediately af-
ter power on and at returning from the stop mode. When switching
the mode between middle/high-speed and low-speed, set the fre-
quency on condition that f(XIN) > 3•f(XCIN).
(4) Low power dissipation mode
The low power consumption operation can be realized by stopping
the main clock XIN in low-speed mode. To stop the main clock, set
bit 5 of the CPU mode register to “1.” When the main clock XIN is
restarted (by setting the main clock stop bit to “0”), set sufficient
time for oscillation to stabilize.
The sub-clock XCIN-XCOUT oscillating circuit can not directly input
clocks that are generated externally. Accordingly, make sure to
cause an external resonator to oscillate.
Oscillation Control
(1) Stop mode
If the STP instruction is executed, the internal clock φ stops at an
“H” level, and XIN and XCIN oscillation stops. When the oscillation
stabilizing time set after STP instruction released bit is “0,” the
prescaler 12 is set to “FF16” and timer 1 is set to “0116.” When the
oscillation stabilizing time set after STP instruction released bit is
“1,” set the sufficient time for oscillation of used oscillator to stabi-
lize since nothing is set to the prescaler 12 and timer 1.
Either XIN or XCIN divided by 16 is input to the prescaler 12 as
count source. Oscillator restarts when an external interrupt is re-
ceived, but the internal clock φ is not supplied to the CPU (remains
at “H”) until timer 1 underflows. The internal clock φ is supplied for
the first time, when timer 1 underflows. This ensures time for the
clock oscillation using the ceramic resonators to be stabilized.
When the oscillator is restarted by reset, apply “L” level to the
RESET pin until the oscillation is stable since a wait time will not
be generated.
(2) Wait mode
If the WIT instruction is executed, the internal clock φ stops at an
“H” level, but the oscillator does not stop. The internal clock φ re-
starts at reset or when an interrupt is received. Since the oscillator
does not stop, normal operation can be started immediately after
the clock is restarted.
To ensure that the interrupts will be received to release the STP or
WIT state, their interrupt enable bits must be set to “1” before ex-
ecuting of the STP or WIT instruction.
When releasing the STP state, the prescaler 12 and timer 1 will
start counting the clock XIN divided by 16. Accordingly, set the
timer 1 interrupt enable bit to “0” before executing the STP instruc-
tion.
sNote
When using the oscillation stabilizing time set after STP instruction
released bit set to “1”, evaluate time to stabilize oscillation of the
used oscillator and set the value to the timer 1 and prescaler 12.
XCIN XCOUT XIN XOUT
Rf _Rd
CCIN CCOUT CIN COUT
Fig. 39 Ceramic resonator circuit
XCIN XCOUT XIN XOUT
Rf
CCIN
Open
Rd
External oscillation
circuit
CCOUT
Vcc
Vss
Fig. 40 External clock input circuit
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