SN74ALS646 Datasheet, PDF (1/29 Pages) Texas Instruments – OCTAL BUS TRANSCEIVERS AND REGISTERS WITH 3-STATE OUTPUTS

SN54ALS646, SN54ALS648, SN54AS646
SN74ALS646A, SN74ALS648A, SN74AS646, SN74AS648
OCTAL BUS TRANSCEIVERS AND REGISTERS WITH 3-STATE OUTPUTS
SDAS039F – DECEMBER 1983 – REVISED JANUARY 1995
• 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
DEVICE
SN54ALS646, SN74ALS646A, ′AS646
SN54ALS648, SN74ALS648A, SN74AS648
OUTPUT
3 state
3 state
LOGIC
True
Inverting
description
SN54ALS646, SN54ALS648, SN54AS646 . . . JT PACKAGE
SN74ALS646A, SN74ALS648A, SN74AS646,
SN74AS648 . . . DW OR NT PACKAGE
(TOP VIEW)
CLKAB 1
SAB 2
DIR 3
A1 4
A2 5
A3 6
A4 7
A5 8
A6 9
A7 10
A8 11
GND 12
24 V_CC
23 CLKBA
22 SBA
21 OE
20 B1
19 B2
18 B3
17 B4
16 B5
15 B6
14 B7
13 B8
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 high-
impedance port may be stored in either or both
registers.
SN54ALS646, SN54ALS648, SN54AS646 . . . FK PACKAGE
(TOP VIEW)
4 3 2 1 28 27 26
A1 5
25 ^OE
A2 6
24 B1
A3 7
23 B2
NC 8
22 NC
A4 9
21 B3
A5 10
20 B4
A6 ¹¹¹² _{13 14 15 16 17 1819} B5
The select-control (SAB and SBA) inputs can
multiplex stored and real-time (transparent mode)
NC – No internal connection
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 I_OL 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.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
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Copyright © 1995, Texas Instruments Incorporated
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