82C55 datasheet(12/23 Pages) INTEL

12 / 23 page

82C55A

Output Control Signal Definition

OBF (Output Buffer Full FF)

The OBF output will

go ‘‘low’’ to indicate that the CPU has written data

out to the specified port The OBF FF will be set by

the rising edge of the WR input and reset by ACK

Input being low

ACK (Acknowledge Input)

A ‘‘low’’ on this input

informs the 82C55A that the data from Port A or Port

B has been accepted In essence a response from

the peripheral device indicating that it has received

the data output by the CPU

INTR (Interrupt Request)

A ‘‘high’’ on this output

can be used to interrupt the CPU when an output

device has accepted data transmitted by the CPU

INTR is set when ACK is a ‘‘one’’ OBF is a ‘‘one’’

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

INTE A

Controlled by bit setreset of PC6

INTE B

Controlled by bit setreset of PC2

231256 – 15

Figure 10 MODE 1 Output

231256 – 16

Figure 11 MODE 1 (Strobed Output)

82C55 Datasheet(PDF) 12 Page - Intel Corporation