8255A-5 データシートの表示（PDF） - Intel

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8255A-5

CHMOS PROGRAMMABLE PERIPHERAL INTERFACE

Intel 

Input Control Signal Definition

STB (Strobe Input) A ‘‘low’’ on this input loads

data into the input latch

IBF (Input Buffer Full F F)

A ‘‘high’’ on this output indicates that the data has

been loaded into the input latch in essence an ac-

knowledgement IBF is set by STB input being low

and is reset by the rising edge of the RD input

INTR (Interrupt Request)

A ‘‘high’’ on this output can be used to interrupt the

CPU when an input device is requesting service

INTR is set by the STB is a ‘‘one’’ IBF is a ‘‘one’’

and INTE is a ‘‘one’’ It is reset by the falling edge of

RD This procedure allows an input device to re-

quest service from the CPU by simply strobing its

data into the port

INTE A

Controlled by bit set reset of PC4

INTE B

Controlled by bit set reset of PC2

82C55A

231256 – 13

Figure 8 MODE 1 Input

Figure 9 MODE 1 (Strobed Input)

231256 – 14

11

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