4551 datasheet(39/69 Pages) RENESAS

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MITSUBISHI MICROCOMPUTERS

4551 Group

SINGLE-CHIP 4-BIT CMOS MICROCOMPUTER for

INFRARED REMOTE CONTROL TRANSMITTER

LIST OF PRECAUTIONS

Noise and latch-up prevention

Connect a capacitor on the following condition to prevent noise

and latch-up;

• connect a bypass capacitor (approx. 0.1

µF) between pins

VDD and VSS at the shortest distance,

• equalize its wiring in width and length, and

• use the thickest wire.

In the built-in PROM version, CNVSS pin is also used as VPP

pin. Accordingly, when using this pin, connect this pin to VSS

through a resistor about 5 k

Ω (connect this resistor to CNVSS/

VPP pin as close as possible).

Prescaler

Stop the prescaler operation to change its frequency dividing

ratio.

Count source

Stop timer 1 or timer LC counting to change its count source.

When timer 2 count source changes from f(XCIN) to ORCLK

(W23 = “0”

→ W23 = “1”), the count value of timer 2 is initialized.

However, when timer 2 count source changes from ORCLK to

f(XCIN) (W23 = “1”

→ W23 = “0”) or the same count source is

set again (W23 = “0”

→ W23 = “0” or W23 = “1” → W23 = “1”),

the count value of timer 2 is not initialized.

Timer 2

Timer 2 has the watchdog timer function (WDT). When timer 2

is used as the WDT, note that the processing to initialize the

count value and the execution of the WRST instruction.

Reading the count value

Stop the prescaler and then execute the TAB1 instruction to

read timer 1 data.

Writing to reload register R1

Write the data to reload register R1 while timer 1 is operating,

avoid a timing when timer 1 underflows.

Notes when using the carrier wave output auto-control function

• Execute the STCR instruction after setting the timer 1 and

operation.

• Stop the timer 1 (W20=“0”) after stopping the carrier

generating circuit (SPCR instruction executed) while the

carrier wave output is disabled in order to stop the carrier

wave output auto-control operation.

• If the carrier wave output auto-control function is invalidated

(C20=“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. This

state is released by timer 1 stop (W20=“0”).

When the carrier wave output auto-control function is

validated (C20=“1”) again after it is invalidated (C20=“0”),

the auto-control of carrier wave output is started again when

the next timer 1 underflow occurs. However, when the carrier

wave output auto-control bit is changed during timer 1

underflow, the error-operation may occur.

• Use the carrier wave or the carrier wave divided by 2 as the

timer 1 count source when the carrier wave output auto-

control function is selected.

If the ORCLK is used as the count source, a hazard may

occur in port CARR output because ORCLK is not

synchronized with the carrier wave.

D5/INT pin

When the interrupt valid waveform of D5/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 D5/INT pin with the bit 2 of register

I1 (refer to Figure 40).

• 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 40). Depending on the input

state of the D5/INT pin, the external 0 interrupt request flag

(EXF0) may be set to “1” when the interrupt valid waveform

is changed.

; (!!!02)

TV1A

; The SNZ0 instruction is valid

TI1A

; Change of the interrupt valid waveform

NOP

SNZ0

;The SNZ0 instruction is executed

NOP

! : this bit is not related to the setting of INT.

...

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 D5 output function can be used even when

INT function is selected.

Power down instruction (POF instruction, POF2 instruction)

Execute the POF or POF2 instruction immediately after

executing the EPOF instruction to enter the power down state.

Note that system cannot enter the power down state when

executing only the POF or POF2 instruction.

Program counter

Make sure that the PCH does not specify after the last page of

the built-in ROM.

Fig. 40 External 0 interrupt program example

4551 Datasheet(PDF) 39 Page - Renesas Technology Corp

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