M38B53M4-059FP datasheet(95/355 Pages) MITSUBISHI

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2-7

APPLICATION

2.1 I/O port

38B5 Group User’s Manual

2.1.4 Notes on use

(1)

Notes in standby state

In standby state

V1 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 open-drain 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 points:

• External circuit

• Variation of output levels during the ordinary operation

When using built-in pull-up 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 flowing out to external

q Reason

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

• P-channel......when the content of the port latch is “0”

• N-channel......when the content of the 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 a input port and an I/O port are “undefined”. This may cause power source

current.

V1 standby state: stop mode by executing STP instruction

wait mode by executing WIT instruction

(2)

N-channel open-drain port

P40–P42, P45, P46, P60 of N-channel open-drain output ports have the built-in hysteresis circuit for

input. In standby state for low-power dissipation, do not make these pins floating state.

q Reason

When power sources for pull-up of these pins are cut off in standby state, these ports become

floating. Accordingly, a current may flow from Vcc to Vss through the built-in hysteresis circuit.

M38B53M4-059FP Datasheet(PDF) 95 Page - Mitsubishi Electric Semiconductor