M37544G Mitsubishi Electric, M37544G Datasheet - Page 34

• Manufacturer Part Number: M37544G
• Description: Single-Chip 8-Bit CMOS Microcomputer
• Manufacturer: Mitsubishi Electric

(1) Oscillation control
• Stop mode
When the STP instruction is executed, the internal clock
an “H” level and the X
to “01
bilization time set bit after release of the STP instruction is “0”. On
the other hand, timer 1 and prescaler 1 are not set when the
above bit is “1”. Accordingly, set the wait time fit for the oscillation
stabilization time of the oscillator to be used. Single selected by
the timer1countsource selection bit is connected to the input of
prescaler 1. When an external interrupt is accepted, oscillation is
restarted but the internal clock
underflows. As soon as timer 1 underflows, the internal clock
supplied. This is because when a ceramic / quartz-crystal oscilla-
tor is used, some time is required until a start of oscillation. In
case oscillation is restarted by reset, no wait time is generated. So
apply an “L” level to the RESET pin while oscillation becomes
stable.
Also, the STP instruction cannot be used while CPU is operating
by a ring oscillator.
• Wait mode
If the WIT instruction is executed, the internal clock
“H” level, but the oscillator does not stop. The internal clock re-
starts if a reset occurs or when an interrupt is received. Since the
oscillator does not stop, normal operation can be started immedi-
ately 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.
For use with the oscillation stabilization set bit after release of the
STP instruction set to “1”, set values in timer 1 and prescaler 1 af-
ter fully appreciating the oscillation stabilization time of the
oscillator to be used.
• Switch of ceramic / quartz-crystal and RC oscillations
After releasing reset the operation starts by starting a built-in ring
oscillator. Then, a ceramic / quartz-crystal oscillation or an RC os-
cillation is selected by setting bit 5 of the CPU mode register.
• Double-speed mode
When a ceramic / quartz-cfystal oscillation is selected, a double-
speed mode can be used. Do not use it when an RC oscillation is
selected.
• CPU mode register
Bits 5, 1 and 0 of CPU mode register are used to select oscillation
mode and to control operation modes of the microcomputer. In or-
der to prevent the dead-lock by error-writing (ex. program
run-away), these bits can be rewritten only once after releasing re-
set. After rewriting it is disable to write any data to the bit. (The
emulator MCU “M37544RSS” is excluded.)
Also, when the read-modify-write instructions (SEB, CLB) are ex-
ecuted to bits 2 to 4, 6 and 7, bits 5, 1 and 0 are locked.
34
Notes on clock generating circuit
16
” and prescaler 1 is set to “FF
IN
oscillator stops. At this time, timer 1 is set
______
remains at “H” until timer 1
16
” when the oscillation sta-
stops at an
stops at
is
• Clock division ratio, X
The state transition shown in Fig. 46 can be performed by setting
the clock division ratio selection bits (bits 7 and 6), X
control bit (bit 4), ring oscillator oscillation control bit (bit 3) of CPU
mode register. Be careful of notes on use in Fig. 46.
Fig. 42 Structure of CPU mode register
b7
Note 1: The bit can be rewritten only once after releasing reset. After rewriting
2: These bits are used only when a ceramic / quartz-crystal oscillation is selected.
Do not use these when an RC oscillation is selected.
it is disable to write any data to the bit. However, by reset the bit is
initialized and can be rewritten, again.
(It is not disable to write any data to the bit for emulator MCU
“M37544RSS”.)
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
IN
b0
oscillation control, ring oscillator control
CPU mode register
(CPUM: address 003B
Processor mode bits (Note 1)
Stack page selection bit
Ring oscillator oscillation control bit
X
Oscillation mode selection bit (Note 1)
Clock division ratio selection bits
b1 b0
IN
b7 b6
0
0
1
1
0 : 0 page
1 : 1 page
0 : Ring oscillator oscillation enabled
1 : Ring oscillator oscillation stop
0 : Ceramic / quartz-crystal or RC oscillation enabled
1 : Ceramic / quartz-crystal or RC oscillation stop
0 : Ceramic / quartz-crystal oscillation
1 : RC oscillation
0
0
1
1
oscillation control bit
0 Single-chip mode
1
0
1
0 : f( ) = f(X
1 : f( ) = f(X
0 : applied from ring oscillator
1 : f( ) = f(X
Not available
16
IN
IN
IN
, initial value: 80
)/2 (High-speed mode)
)/8 (Middle-speed mode)
) (Double-speed mode)(Note 2)
7544 Group
16
)
IN
oscillation