7 Detailed Description

7.1 Overview

The CD54HC245, CD54HCT245, and CD74HC245, CD74HCT245 are high-speed octal three-state bidirectional

transceivers intended for two-way asynchronous communication between data buses. They have high drive

current outputs which enable high-speed operation while driving large bus capacitances. They provide the low

power consumption of standard CMOS circuits with speeds and drive capabilities comparable to that of LSTTL

circuits.

The CD54HC245, CD54HCT245, CD74HC245 and CD74HCT245 allow data transmission of the B bus or from

the B bus to the A bus. The logic level at the direction input (DIR) determines the direction. The output enable

input (OE), when high, puts the I/O ports in the high-impedance state.

The HC/HCT245 is similar in operation to the HC/HCT640 and the HC/HCT643.

Functional Block Diagram

7.2 Device Functional Modes

Table 7-1. Truth Table

Control Inputs(1)

Operation

OE

DIR

L

L

B Data to A

Bus

L

H

A Data to B

Bus

H

X

Isolation

(1)

H = High Level, L = Low

Level, X = Irrelevant

CD54HC245, CD74HC245, CD54HCT245, CD74HCT245

SCHS119B – NOVEMBER 1998 – REVISED JULY 2022

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