M38B53M4-059FP datasheet(96/355 Pages) MITSUBISHI

96 / 355 page

2-8

38B5 Group User’s Manual

APPLICATION

2.1 I/O port

(3)

Modifying port latch of I/O port with bit managing instruction

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

V2, the value of the

unspecified bit may be changed.

q Reason

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.

V2 Bit managing instructions: SEB and CLB instructions

(4)

Pull-up control

When each port which has built-in pull-up resistor (P5, P61–P65, P7, P84–P87, P9) is set to output

port, pull-up control of corresponding port become invalid. (Pull-up cannot be set.)

q Reason

Pull-up control is valid only when each direction register is set to the input mode.

2.1.5 Termination of unused pins

(1)

Terminate unused pins

Output ports : Open

Input ports :

Connect each pin to VCC or VSS through each resistor of 1 k

Ω to 10 kΩ.

As for pins whose potential affects to operation modes such as pin INT or others, select the VCC

pin or the VSS pin according to their operation mode.

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.

M38B53M4-059FP Datasheet(PDF) 96 Page - Mitsubishi Electric Semiconductor

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