SN74ALS870 Datasheet, PDF (1/7 Pages) Texas Instruments – DUAL 16-BY-4 REGISTER FILES

SN74ALS870
DUAL 16-BY-4 REGISTER FILES
• 3-State Buffer-Type Outputs Drive Bus
Lines Directly
• Each Register File Has Individual
Write-Enable Controls and Address Lines
• Designed Specifically for Multibus
Architecture and Overlapping File
Operations
• Prioritized B-Input Port Prevents Write
Conflicts During Dual-Input Mode
• Package Options Include Plastic
Small-Outline (DW) Packages and Standard
Plastic (NT) 300-mil DIPs
description
SDAS139A – DECEMBER 1982 – REVISED JANUARY 1995
DW OR NT PACKAGE
(TOP VIEW)
S0 1
1A0 2
1A1 3
1A2 4
1A3 5
1W 6
S2 7
DQA1 8
DQA2 9
DQA3 10
DQA4 11
GND 12
24 V_CC
23 S1
22 2A3
21 2A2
20 2A1
19 2A0
18 2W
17 S3
16 DQB4
15 DQB3
14 DQB2
13 DQB1
This device features two 16-word by 4-bit register
files. Each register file has individual write-enable
(1W, 2W) controls and address lines. This device has two 4-bit data I/O ports (DQA1–DQA4 and DQB1–DQB4).
The data I/O ports can output to bus A and bus B, receive input from bus A and bus B, receive input from bus
A and output to bus B, or output to bus A and receive input from bus B. To prevent writing conflicts in the
dual-input mode, the B-input port takes priority. Two select (S0 and S1) lines control which port has access to
which register. S2 determines whether the A ports are in the input or the output modes and S3 does likewise
for the B ports. The address lines (1A0 –1A3 or 2A0 –2A3) are decoded by an internal 1-of-16 decoder to select
which register word is to be accessed. All outputs are 3-state buffer-type outputs designed specifically to drive
bus lines directly.
The SN74ALS870 is characterized for operation from 0°C to 70°C.
FUNCTION TABLE
FILE SELECT
INPUT/OUTPUT
S0 S1
FILE SEL
S2 S3 I/O SEL
L L 1R to A, 1R to B
H L 2R to A, 1R to B
L
L H 1R to A, 2R to B
L A out, B out
H H 2R to A, 2R to B
L L A to 1R, 1R to B
H L A to 2R, 1R to B
H L A in, B out
L H A to 1R, 2R to B
H H A to 2R, 2R to B
L L 1R to A, B to 1R
H L 2R to A, B to 1R
L H A out, B in
L H 1R to A, B to 2R
H H 2R to A, B to 2R
LL
B to 1R
H L A to 2R, B to 1R
HH
L H A to 1R, B to 2R
A in, B in
HH
B to 2R
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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