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7641

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

Mitsumi 

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MITSUBISHI MICROCOMPUTERS

7641 Group

SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER

USAGE NOTES

Oscillator Connection Notice

The built-in feedback register (400 Ω) is internally connected be-

tween pins XIN and XOUT.

Power Supply Pins Treatment Notice

Please connect 0.1 µF and 4.7 µF capacitors in parallel between

pins Vcc and Vss, and pins AVss and AVcc.

These capacitors must be connected as close as possible be-

tween the DC supply and GND pins, and also the analog supply

pin and corresponding GND pin.

Wiring patterns for these supply and GND pins must be wider than

other signal patterns.

These filter capacitors should not be placed near the LPF pins as

they will cause noise problems

Rest Pin Treatment Notice (Noise

Elimination)

If the reset input signal rises very slowly, we recommend attaching

a capacitor, such as a 1000 pF ceramic capacitor with excellent

high frequency characteristics, between the RESET pin and the

Vss pin.

Please note the following two issues for this capacitor connection.

(1) Capacitor wiring pattern must be as short as possible (within

20 mm).

(2) The user must perform an application level operation test.

LPF Pin Treatment Notice

All passive components must be located as close as possible to

the LPF pin.

LPF pin

1 kΩ

680 pF

AVSS pin

0.1 µF

Fig. 124 Passive components near LPF pin

AVss and AVcc Pin Treatment Notice (Noise

Elimination)

An insulation connector (Ferrite Beads) must be connected be-

tween AVss and Vss pins and between AVcc and Vcc pins.

USB Transceiver Treatment (Noise

Elimination)

•The USB specification ver. 1.1 requires a driver -impedance 28 to

44 Ω. (Refer to Clause 7.1.1.1 Full-speed (12 Mb/s) Driver Char-

acteristics in the USB specification.) In order to meet the USB

specification impedance requirements, connect a resistor (27 Ω

to 33 Ω recommended) in series between the USB D+ pin and the

USB D- pin.

In addition, in order to reduce the ringing and control the falling/

rising timing of USB D+/D- and a crossover point, connect a ca-

pacitor between the USB D+/D- pins and the Vss pin if necessary.

The values and structure of those peripheral elements depend on

the impedance characteristics and the layout of the printed circuit

board. Accordingly, evaluate your system and observe waveforms

before actual use and decide use of elements and the values of

resistors and capacitors.

•Connect a capacitor between the Ext. Cap. pin and the Vss pin.

The capacitor should have a 2.2 µF capacitor (Tantalum capaci-

tor) and a 0.1 µF capacitor (ceramic capacitor) connected in

parallel. Figure 125 for the proper positions of the peripheral

components.

Frequency Synthesizer

USBC5

DC-DC converter

XIN

enable

lock enable

current

enable

mode

FSE

LS

USBC4

USBC3

Ext. Cap.

USB Clock USB FCU

(48 MHz) enable

USBC7

USB

transceiver

enable

USBC7

D+

D-

Note 2

Notes 1: In Vcc = 3.3 V, connect to Vcc.

2: The resistors values depend on the layout of the printed circuit board.

Fig.125 Peripheral circuit

Note 1

•In Vcc = 3.3 V operation, connect the Ext. Cap. pin directly to the

Vcc pin in order to supply power to the USB transceiver. In addi-

tion, you will need to disable the DC-DC converter in this

operation (set bit 4 of the USB control register to “0”.) If you are

using the bus powered supply in Vcc = 3.3 V operation, the DC-

DC converter must be placed outside the MCU.

•Make sure the USB D+/D- lines do not cross any other wires.

Keep a large GND area to protect the USB lines. Also, make sure

you use a USB specification compliant connecter for the connec-

tion.

145

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