M38203M4 Datasheet, PDF (58/344 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

MITSUBISHI MICROCOMPUTERS
3820 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
CLOCK GENERATING CIRCUIT
The 3820 group has two built-in oscillation circuits. An oscillation
circuit can be formed by connecting a resonator between XIN and
XOUT (XCIN and XCOUT). Use the circuit constants in accordance
with the resonator manufacturer's recommended values. No exter-
nal resistor is needed between XIN and XOUT since a feed-back re-
sistor exists on-chip. However, an external feed-back resistor is
needed between XCIN and XCOUT.
To supply a clock signal externally, input it to the XIN pin and make
the XOUT pin open. The sub-clock XCIN-XCOUT oscillation circuit
cannot directly input clocks that are externally generated. Accord-
ingly, be sure to cause an external resonator to oscillate.
Immediately after poweron, only the XIN oscillation circuit starts
oscillating, and XCIN and XCOUT pins function as I/O ports. The
pull-up resistor of XCIN and XCOUT pins must be made invalid to
use the sub-clock.
Frequency Control
Middle-speed mode
The internal clock φ is the frequency of XIN divided by 8.
After reset, this mode is selected.
High-speed mode
The internal clock φ is half the frequency of XIN.
Low-speed mode
• ^{The internal clock φ is half the frequency of XCIN.}
• ^{A low-power consumption operation can be realized by stopping}
the main clock XIN in this mode. To stop the main clock, set bit 5
of the CPU mode register to “1”.
When the main clock XIN is restarted, set enough time for oscil-
lation to stabilize by programming.
Note: If you switch the mode between middle/high-speed and low-
speed, stabilize both XIN and XCIN oscillations. The suffi-
cient time is required for the sub-clock to stabilize, espe-
cially immediately after poweron and at returning from stop
mode. When switching the mode between middle/high-
speed and low-speed, set the frequency on condition that
f(XIN)>3f(XCIN).
Oscillation Control
Stop mode
If the STP instruction is executed, the internal clock φ stops at an
“H” level, and XIN and XCIN oscillators stop. Timer 1 is set to “FF16”
and timer 2 is set to “0116”.
Either XIN or XCIN divided by 16 is input to timer 1 as count
source, and the output of timer 1 is connected to timer 2.
The bits of the timer 123 mode register except bit 4 are cleared to
“0”. Set the timer 1 and timer 2 interrupt enable bits to disabled
(“0”) before executing the STP instruction.
Oscillator restarts at reset or when an external interrupt is re-
ceived, but the internal clock φ is not supplied to the CPU until
timer 2 underflows. This allows time for the clock circuit oscillation
to stabilize.
Wait mode
If the WIT instruction is executed, the internal clock φ stops at an
“H” level. The states of XIN and XCIN are the same as the state be-
fore the executing the WIT instruction. The internal clock restarts
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.
XCIN XCOUT XIN XOUT
Rf _Rd
CCIN
CCOUT CIN COUT
Fig. 42 Ceramic resonator circuit
XCIN XCOUT
XIN XOUT
CCIN
Rf _Rd
Open
External oscillation
CCOUT circuit
VCC
VSS
Fig. 43 External clock input circuit
1-42
3820 GROUP USER’S MANUAL