SN54HCT646, SN74HCT646
OCTAL BUS TRANSCEIVERS AND REGISTERS
WITH 3-STATE OUTPUTS
SCLS178B – MARCH 1984 – REVISED MAY 1997
SN54HCT646 . . . JT OR W PACKAGE
SN74HCT646 . . . DW OR NT PACKAGE
(TOP VIEW)
Inputs Are TTL-Voltage Compatible
Independent Registers for A and B Buses
Multiplexed Real-Time and Stored Data
True Data Paths
CLKAB
SAB
DIR
A1
A2
A3
A4
A5
A6
A7
A8
GND
V
CC
1
24
23
22
21
20
19
18
17
16
15
14
13
CLKBA
SBA
OE
B1
B2
B3
B4
B5
B6
B7
2
High-Current 3-State Outputs Can Drive up
to 15 LSTTL Loads
3
4
Package Options Include Plastic
Small-Outline (DW) and Ceramic Flat (W)
Packages, Ceramic Chip Carriers (FK), and
Standard Plastic (NT) and Ceramic (JT)
300-mil DIPs
5
6
7
8
9
10
11
12
description
B8
The ’HCT646 consist of bus-transceiver circuits
with 3-state outputs, D-type flip-flops, and control
circuitry arranged for multiplexed transmission of
data directly from the input bus or from the internal
registers. DataontheAorBbusisclockedintothe
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 ’HCT646.
SN54HCT646 . . . FK PACKAGE
(TOP VIEW)
4
3
2
1
28 27 26
25
A1
A2
A3
NC
A4
OE
B1
B2
NC
B3
B4
B5
5
6
7
8
9
24
23
22
21
20
19
Output-enable (OE) and direction-control (DIR)
inputs control the transceiver functions. In the
transceiver mode, data present at the
high-impedance port can be stored in either or
both registers.
A5 10
11
A6
12 13 14 15 16 17 18
The select-control (SAB and SBA) inputs can
multiplex stored and real-time (transparent mode)
data. DIR determines which bus receives data
when OE is active (low). In the isolation mode (OE
high), A data can be stored in one register and/or
B data can be stored in the other register.
NC – No internal connection
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, can be driven at a time.
The SN54HCT646 is characterized for operation over the full military temperature range of –55°C to 125°C.
The SN74HCT646 is characterized for operation from –40°C to 85°C.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 1997, Texas Instruments Incorporated
UNLESS OTHERWISE NOTED this document contains PRODUCTION
DATA information 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.
1
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