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M37641

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

MITSUBISHI ELECTRIC  

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MITSUBISHI MICROCOMPUTERS

7641 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Clock Input/Output Pin Wiring (Noise

Elimination)

(1) Make the wiring for the input/output pins as short as possible.

(2) Make the wiring across the grounding lead of the capacitor

which is connected to an oscillator and the Vss pin of the MCU

as short as possible (within 20 mm)

(3) Make sure to isolate the oscillation Vss pattern from other pat-

terns for oscillation circuit-use only.

Oscillator Wiring (Noise Elimination)

(1) Keeping oscillator away from large current signal lines

Install a microcomputer (and especially an oscillator) as far as

possible from signal lines, including USB signal lines, where a cur-

rent larger than the tolerance of current value flows. When a large

current flows through those signal lines, strong noise occurs be-

cause of mutual inductance.

(2) Installing oscillator away from signal lines where potential

levels change frequently

Install an oscillator and a connecting pattern of an oscillator away

from signal lines where potential levels change frequently. Also, do

not cross such signal lines over the clock lines or the signal lines

which are sensitive to noise.

Terminate Unused Pins

(1) Output ports : Open

(2) Input ports :

Connect each pin to Vcc or Vss through each resistor of 1 kΩ to

10 kΩ.

Ports that permit the selecting of a built-in pull-up or pull-down re-

sistor can also use this resistor. As for pins whose potential affects

to operation modes such as pins CNVss, INT or others, select the

Vcc pin or the Vss pin according to their operation mode.

(3) I/O ports :

• Set the I/O ports for the input mode and connect them to Vcc or

Vss through each resistor of 1 kΩ to 10 kΩ.

Ports that permit the selecting of a built-in pull-up or pull-down re-

sistor can also use this resistor. Set the I/O ports for the output

mode and open them at “L” or “H”.

• When opening them in the output mode, the input mode of the

initial status remains until the mode of the ports is switched over

to the output mode by the program after reset. Thus, the potential

at these pins is undefined and the power source current may in-

crease in the input mode. With regard to an effects on the

system, thoroughly perform system evaluation on the user side.

• Since the direction register setup may be changed because of a

program runaway or noise, set direction registers by program pe-

riodically to increase the reliability of program.

• At the termination of unused pins, perform wiring at the shortest

possible distance (20 mm or less) from microcomputer pins.

DATA REQUIRED FOR MASK ORDERS

The following are necessary when ordering a mask ROM produc-

tion:

1. Mask ROM Order Confirmation Form

2. Mark Specification Form

3. Data to be written to ROM, in EPROM form (three identical cop-

ies) or one floppy disk.

For the mask ROM confirmation and the mark specifications, refer

to the “Mitsubishi MCU Technical Information” Homepage:

http://www.infomicom.maec.co.jp

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