M38039G8HKP datasheet(85/92 Pages) RENESAS

85 / 92 page

Rev.1.10

Nov 14, 2005

Page 85 of 91

REJ03B0166-0110

3803 Group (Spec.H QzROM version)

PRELIMINARY

Notice: This is not a final specification.

Some parametric limits are subject to change.

NOTES ON PERIPHERAL FUNCTIONS

Notes on Input and Output Ports

1. Notes in standby state

In standby state*1 for low-power dissipation, do not make input

levels of an I/O port “undefined”. Even when an I/O port of

Nchannel open-drain is set as output mode, if output data is “1”,

the aforementioned notes are necessary.

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

Exclusive input ports are always in a high-impedance state. An

output transistor becomes an OFF state when an I/O port is set as

input mode by the direction register, so that the port enter a

highimpedance state. At this time, the potential which is input to

the input buffer in a microcomputer is unstable in the state that

input levels are “undefined”. This may cause power source

current.

Even when an I/O port of N-channel open-drain is set as output

mode by the direction register, if the contents of the port latch is

“1”, the same phenomenon as that of an input port will occur.

NOTES:

1. Standby state : stop mode by executing STP instruction

wait mode by executing WIT instruction

2. Modifying output data with bit managing instruction

When the port latch of an I/O port is modified with the bit

managing instruction*2, the value of the unspecified bit may be

changed.

The bit managing instructions are read-modify-write form

instructions for reading and writing data by a byte unit.

Accordingly, when these instructions are executed on a bit of the

port latch of an I/O port, the following is executed to all bits of

the port latch.

• As for bit which is set for input port:

The pin state is read in the CPU, and is written to this bit after

bit managing.

• As for bit which is set for output port:

The bit value is read in the CPU, and is written to this bit after

bit managing.

Note the following:

• Even when a port which is set as an output port is changed for

an input port, its port latch holds the output data.

• As for a bit of which is set for an input port, its value may be

changed even when not specified with a bit managing

instruction in case where the pin state differs from its port latch

contents.

NOTES:

2. Bit managing instructions : SEB, and CLB instructions

Termination of Unused Pins

1. Terminate unused pins

(1) Output ports : Open

(2) I/O ports :

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

or VSS through each resistor of 1 k

Ω to 10 kΩ.

Ports that permit the selecting of a built-in pull-up resistor 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 increase 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

periodically to increase the reliability of program.

(3) The AVSS pin when not using the A/D converter :

• When not using the A/D converter, handle a power source pin

for the A/D converter, AVSS pin as follows:

AVSS: Connect to the VSS pin.

2. Termination remarks

(1) I/O ports :

Do not open in the input mode.

• The power source current may increase depending on the

firststage circuit.

• An effect due to noise may be easily produced as compared

with proper termination (2) in 1 and shown on the above.

(2) I/O ports :

When setting for the input mode, do not connect to VCC or VSS

directly.

If the direction register setup changes for the output mode

because of a program runaway or noise, a short circuit may occur

between a port and VCC (or VSS).

(3) I/O ports :

When setting for the input mode, do not connect multiple ports in

a lump to VCC or VSS through a resistor.

If the direction register setup changes for the output mode

because of a program runaway or noise, a short circuit may occur

between ports.

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

shortest possible distance (20 mm or less) from micro-

computer pins.

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