M38002M4 Datasheet, PDF (42/173 Pages) Mitsubishi Electric Semiconductor – 8-BIT SINGLE-CHIP MICROCOMPUTER

HARDWARE
FUNCTIONAL DESCRIPTION
Clock Generating Circuit
An oscillation circuit can be formed by connecting a resonator be-
tween XIN and XOUT. To supply a clock signal externally, input it to
the XIN pin and make the XOUT pin open.
Oscillation control
Stop Mode
If the STP instruction is executed, the internal clock φ stops at “H”.
Timer 1 is set to “0116” and prescaler 12 is set to “FF16”.
Oscillator restarts when an external interrupt is received, but the
internal clock φ remains at “H” until timer 1 underflows.
This allows time for the clock circuit oscillation to stabilize.
If oscillator is restarted by a reset, no wait time is generated, so
keep the RESET pin at “L” level until oscillation has stabilized.
Wait Mode
If the WIT instruction is executed, the internal clock φ stops at an
“H” level, but the oscillator itself does not stop. The internal clock
restarts if a reset occurs 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 interrupts will be received to release the STP or
WIT state, interrupt enable bits must be set to “1” before the STP
or WIT instruction is executed.
When the STP status is released, prescaler 12 and timer 1 will
start counting and reset will not be released until timer 1
underflows, so set the timer 1 interrupt enable bit to “0” before the
STP instruction is executed.
XIN
XOUT
CIN
Fig. 25 Ceramic resonator circuit
COUT
XIN
XOUT
Open
External oscillation
Vcc
circuit
Vss
Fig. 26 External clock input circuit
Interrupt request
Interrupt disable
flag (I)
Reset
SQ
SQ
STP instruction R
WIT
instruction
R
QS
Reset
R ^{STP instruction}
ONW pin
Single-chip mode
1/2
Rd
Rf
XIN
XOUT
Fig. 27 Block diagram of clock generating circuit
φ output
ONW
control
1/8
Internal clock φ
Prescaler 12
Timer 1
FF16
0116
Reset or STP instruction
1-28
3800 GROUP USER’S MANUAL