7630 datasheet(185/238 Pages) RENESAS

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3-14

APPENDIX

3.3 Notes on use

7630 Group User’s Manual

3.3.4 Notes on input and output pins

(1) Notes in stand-by state

In stand-by state51 for low-power dissipation, do not make input levels of an input port and an I/O port

“undefined,” especially for I/O ports of the P-channel and the N-channel open-drain.

Pull-up (connect the port to VCC) or pull-down (connect the port to VSS) these ports through a resistor.

When determining a resistance value, note the following:

• External circuit

• Variation of output levels during the ordinary operation

When using built-in pull-up or pull-down resistor, note on varied current values.

• When setting as an input port : Fix its input level.

• When setting as an output port : Prevent current from flow to the external.

51 stand-by state : The stop mode by executing the STP instruction or the wait mode by executing the

WIT instruction

Reason

Even when setting as an output port with its direction register, in the following state :

• P-channel......when the content of the data register (port latch) is “0”

•N-channel......when the content of the data register (port latch) is “1”

the transistor becomes the OFF state, which causes the ports to be the high-impedance state. Note

that the level becomes “undefined” depending on external circuits.

Accordingly, the potential which is input to the input buffer in a microcomputer is unstable in the state

that input levels of an input port and an I/O port are “undefined.” This may cause power source

current.

____________

3.3.3 Notes on RESET pin

____________

In case where the RESET signal rise time is long, connect a ceramic capacitor or others across the RESET

pin and the VSS pin. And use a 1000 pF or more capacitor for high frequency use. When connecting the

capacitor, note the following :

• Make the length of the wiring which is connected to a capacitor as short as possible.

• Be sure to check the operation of application products on the user side.

Reason

____________

If the several nanosecond or several ten nanosecond impulse noise enters the RESET pin, it may cause a

microcomputer failure.

(2) AVSS pin

AVSS pin is the A-D converter power source pin. Regardless of using the A-D conversion function or

not, connect AVSS to the VSS line.

Reason

If the AVSS pin is opened, the microcomputer may have a failure because of noise or others.

(3) Clock frequency during an A-D conversion

The comparator consists of a capacity coupling, and a charge of the capacity will be lost if the clock

frequency is too low. Thus, make sure the following during an A-D conversion.

• f(XIN) is 500 kHz or more.

• Do not execute the STP instruction and WIT instruction.

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