35
MITSUBISHI MICROCOMPUTERS
4570 Group
SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER
LIST OF PRECAUTIONS
Noise and latch-up prevention
Connect a capacitor on the following condition to prevent noise
and latch-up;
connect a capacitor (approx. 0.1
μ
F) between pins V
DD
and
V
SS
at the shortest distance,
equalize its wiring in width and length, and
use the thickest wire.
In the One Time PROM version, CNV
SS
pin is also used as
V
PP
pin. Accordingly, when using this pin, connect this pin to
V
SS
through a resistor about 5 k
(connect this resistor to
CNV
SS
/V
PP
pin as close as possible).
Prescaler
Stop the prescaler operation to change its frequency dividing
ratio.
Count source
Stop timer 1, timer 2 or timer 3 counting to change its count
source.
Reading the timer count value
Stop each of the timers and then execute the TAB1, TAB2 or
TAB3 instruction to read timer 1, 2 or 3 data.
Writing to reload register R1
When writing the data to reload register R1 while timer 1 is
operating, avoid a timing when timer 1 underflows.
Writing to reload register R3H
When writing the data to reload register R3H while timer 3 is
operating, avoid a timing when timer 3 underflows.
Notes on timer 3 operation start
Set the timer 1 and register C2 before timer 3 is started to
operate (W3
3
=“1”).
Notes on carrier wave output auto-control operation stop
Stop the timer 1 (W1
0
=“0”) after stopping the timer 3 (W3
3
=“0”)
while the carrier wave output is disabled in order to stop the
carrier wave output auto-control operation.
Notes on setting carrier wave output control regiter C2
If the carrier wave output auto-control function is invalidated
(C2
0
=“0”) while the carrier wave output is auto-controlled, the
output of port CARR retains the state when the auto-control is
invalidated regardless of timer 1 underflow.
When the carrier wave output auto-control function is validated
(C2
0
=“1”) again after it is invalidated (C2
0
=“0”), the auto-control
by timer 1 is validated again when the next timer 1 underflow
occurs.
However, when the carrier wave output auto-control bit (C2
0
)
is changed during timer 1 underflow, the error-operation may
occur.
Notes on timer 1 count source
When the carrier wave output auto-control function is selected,
use the carrier wave CARRY as the timer 1 count source.
If the ORCLK is used as the count source, a short pulse may
occur in port CARR output because ORCLK is not
synchronized with the carrier wave.
Notes on writing to reload register R1 when carrier wave output
auto-control operation
When the carrier wave output auto-control function is selected
and data is set to reload register R1 while timer 1 is operating,
avoid the timing that the contents of timer 1 becomes “0” to
execute the T1AB instruction.
One Time PROM version
The operating power voltage of the One Time PROM version
is within the range of 2.5 V to 5.5 V.
Multifunction
Note that the port D
9
output function and P2
1
input function
can be used even when T
OUT
and INT pin function is selected.
POF instruction
Note that system cannot enter the RAM back-up state when
executing only the POF instruction.
Execute the POF instruction immediately after executing the
EPOF instruction to enter the RAM back-up.
Be sure to disable interrupts by executing the DI instruction
before executing the EPOF instruction.
Program counter
Make sure that the PC
H
does not specify after the last page of
the built-in ROM.
P2
1
/INT pin
When the interrupt valid waveform of P2
1
/INT pin is changed
with the bit 2 of register I1 in software, be careful about the
following notes.
Clear the bit 0 of register V1 to “0” and then change the
interrupt valid waveform of P2
1
/INT pin with the bit 2 of
register I1 (refer to Figure 34
).
Clear the bit 2 of register I1 to “0” and execute the SNZ0
instruction to clear the EXF0 flag after executing at least
one instruction (refer to Figure 34
). Depending on the input
state of the P2
1
/INT pin, the external 0 interrupt request flag
(EXF0) may be set to “1” when the interrupt valid waveform
is changed.
.
.
11
12
13
14
15
16
LA
TV1A
LA
TI1A
NOP
SNZ0
NOP
.
.
4
; (
0
2
)
; The SNZ0 instruction is valid
4
; Change of the interrupt valid waveform
;The SNZ0 instruction is executed
: this bit is not related to the setting of INT.
Fig. 34 External 0 interrupt program example