Independent Registers for A and B Buses

Multiplexed Real-Time and Stored Data

Choice of True or Inverting Data Paths

Choice of 3-State or Open-Collector

Outputs

Package Options Include Plastic

Small-Outline (DW) Packages, Ceramic

Chip Carriers (FK), and Standard Plastic

(NT) and Ceramic (JT) 300-mil DIPs

description

These devices consist of bus-transceiver circuits

with 3-state or open-collector outputs, D-type

flip-flops, and control circuitry arranged for

multiplexed transmission of data directly from the

data bus or from the internal storage registers.

Data on the A or B bus is clocked into the registers

on the low-to-high transition of the appropriate

clock (CLKAB or CLKBA) input. Figure 1

illustrates the four fundamental bus-management

functions that can be performed with the octal bus

transceivers and registers.

Output-enable (OE) and direction-control (DIR)

inputs control the transceiver functions. In the

transceiver mode, data present at the highimpedance

port may be stored in either or both

registers.

The select-control (SAB and SBA) inputs can

multiplex stored and real-time (transparent mode)

data. The circuitry used for select control eliminates the typical decoding glitch that occurs in a multiplexer during

the transition between stored and real-time data. DIR determines which bus receives data when OE is low. In

the isolation mode (OE high), A data may be stored in one register and/or B data may be stored in the other

register.

When an output function is disabled, the input function is still enabled and can be used to store and transmit

data. Only one of the two buses, A or B, may be driven at a time.

The -1 version of the SN74ALS646A is identical to the standard version, except that the recommended

maximum IOL in the -1 version is increased to 48 mA. There are no -1 versions of the SN54ALS646,

SN54ALS648, or SN74ALS648A.

The SN54ALS646, SN54ALS648, and SN54AS646 are characterized for operation over the full military

temperature range of –55°C to 125°C. The SN74ALS646A, SN74ALS648A, SN74AS646, and SN74AS648 are

characterized for operation from 0°C to 70°C.