74AC648SCX

Series:	74AC
Packaging:	Tape & Reel (TR)
Part Status:	Obsolete
Logic Type:	Transceiver, Non-Inverting
Number of Elements:	1
Number of Bits per Element:	8
Input Type:	--
Output Type:	3-State
Current - Output High, Low:	24mA, 24mA
Voltage - Supply:	2 V ~ 6 V
Operating Temperature:	-40°C ~ 85°C (TA)
Mounting Type:	Surface Mount
Package / Case:	24-SOIC (0.295", 7.50mm Width)
Supplier Device Package:	24-SOIC
Base Part Number:	74AC648

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Logic - Buffers, Drivers, Receivers, Transceivers

Introduction

The 74AC648SCX is a 8-bit buffered remote expansion I/O device with four address pins allowing up to sixteen devices to be connected to the same two-wire-bus (TWB) system with 4-bit addressable device names. It consists of an 8-bit I/O device with an 8-bit latch, a signal receiver and transmitter, and a bus driver. It is an ideal solution for remote signal switching, system expansion, and level conversion. The 74AC648SCX allows two-wire-bus systems to be expanded up to 8-bit wide I/O by directly connecting multiple devices to the same bus and one device can read or write the bus data of other devices. It can also be used as an I/O bridge between other two-wire-bus devices, like the I²C bus, the SPI bus, and the SMBus.

Features

The 74AC648SCX has several features that make it particularly versatile:

• Supports 8-bit I/O devices
• 4-bit addressable device names allowing up to 16 devices to share the same two-wire-bus system
• Compatible with I²C bus, SPI bus, SMBus
• Each device is programmed through the bus address
• On-chip signal receiver and transmitter
• On-chip address pins and two-wire-bus driver
• Very low speed operation (1MHz or less)
• Designed for very low power operation (1mA typical)

The device is specified for operation from −40°C to +85°C and 25°C ambient temperature.

Applications

The 74AC648SCX is mostly used in remote expansion systems and as an inter-bus bridge device. The most common applications are listed as follows:

• Remote control systems
• Cell phones
• Television receivers
• Thin clients
• Robot arms
• CT scanners
• Security systems
• Digital cameras

Working Principle

The 74AC648SCX is a two-wire-bus device that can be Daisy-Chained with up to 16 devices on the same bus and each device is programmed through the bus address. The device consists of an 8-bit I/O device with an 8-bit latch and an on-chip receiver and transmitter, along with four address pins (A0-A3). The bus driver consists of two open-drain N-channel FETs (Q1 and Q2). The operation of the 74AC648SCX is divided into two parts - the address systems and the data system. In the address system, the host computer first sends the address of the device through the bus and then the 74AC648SCX compares it with the on-chip address that is set by the address pins (A0-A3). If the addresses match, then the 74AC648SCX switches on the receiver and transmitter, while if they don’t match, then the receiver and transmitter are switched off. In the data system, the host computer can read or write data to or from the device. The data is sent through the bus to the device and the 74AC648SCX stores the data in its latch. The corresponding I/O lines are then assigned to the latch data. The 74AC648SCX can be used as an I/O bridge device between other two-wire bus devices. It can act as an interface between the I²C bus, the SPI bus, and the SMBus. This allows for remote control and monitoring of I/O devices.

Conclusion

The 74AC648SCX is a 8-bit buffered remote expansion I/O device with four address pins allowing up to sixteen devices to be connected to the same two-wire-bus system. It is most suitable for remote control systems, cell phones, television receivers, Thin clients, robot arms, CT scanners, security systems, and digital cameras. It can also be used as an I/O bridge between the I²C bus, the SPI bus, and the SMBus.

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