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Home > Products > Integrated Circuits (ICs) > Logic > Signal Switches, Multiplexers, Decoders

Texas Instruments SN74ALS870NT

Name: SN74ALS870NT
Brand: Texas Instruments
SKU: SN74ALS870NT
Price: 2.40 USD
Availability: InStock
Rating: 5 (2 reviews)

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Part No.:: SN74ALS870NT

Manufacturer:: Texas Instruments

Category:: Signal Switches, Multiplexers, Decoders

Package:: 24-DIP (0.300", 7.62mm)

Datasheet:: SN74ALS870NT.pdf

Description:: IC REGISTER FILE DL 16X4 24DIP

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Product details

Overview

SN74ALS870NT from Texas Instruments is a dual 16-word × 4-bit register file IC with independent write-enable controls (1W, 2W), 3-state buffer-type outputs, and dedicated A/B I/O ports (DQA1–DQA4, DQB1–DQB4) for bus interfacing in Multibus-compatible systems. It supports overlapping file operations, prioritized B-port write conflict resolution, and operates over 0°C to 70°C at VCC = 4.5–5.5 V.

For engineers reviewing the SN74ALS870NT datasheet, SN74ALS870NT pinout, SN74ALS870NT application, or SN74ALS870NT equivalent, key selection considerations include its dual-register architecture, 24-pin PDIP (NT) package, 3-state output drive capability (IOL = 24 mA), address decoding logic (1A0–1A3 / 2A0–2A3), and S0–S3 port-select control scheme.

Technical Context

The SN74ALS870NT integrates two independent 16×4 RAM arrays with internal 1-of-16 decoders per file, enabling word-select via four address lines per port. Its dual-input mode uses S0/S1 to assign register files to A/B buses while S2/S3 configure directionality (input/output) per port.

Write conflicts are resolved by hardware priority: the B-input port takes precedence during simultaneous A- and B-port writes. All 3-state outputs meet ALS-family timing specs - including tpd ≤ 26 ns (CL = 50 pF), tw ≥ 12 ns, and tsu ≥ 15 ns - and drive bus lines directly without external buffers.

Key Specifications

Parameter	Value and Actual Design Meaning
Memory Size	Two independent 16-word × 4-bit register files - enables concurrent storage and routing of two 4-bit data streams.
Supply Voltage	VCC = 4.5 V to 5.5 V - compatible with standard 5-V TTL/ALS logic rails and ensures stable operation across industrial temperature range.
Output Drive	IOL = 24 mA, IOH = –2.6 mA - sufficient to directly drive multiple TTL loads on shared bus lines without buffering.
Propagation Delay	tpd ≤ 26 ns (DQA ↔ DQB, CL = 50 pF) - supports high-speed register-to-register transfers in real-time control and data acquisition.
Operating Temperature	TA = 0°C to 70°C - rated for commercial-grade embedded systems and industrial controller applications.
Input Thresholds	VIH = 2.0 V min, VIL = 0.8 V max - ensures robust noise margin and compatibility with 5-V CMOS/TTL input logic families.

Pinout & Package

SN74ALS870NT is housed in a 24-pin plastic dual-in-line package (PDIP), 300-mil width, with standard through-hole mounting and 0.1-inch pin pitch. Pin 1 is located at top-left corner when notch faces upward.

Pin/Terminal	Circuit Role	Design Meaning
1	S0	File select control - determines which register file connects to bus A (low = File 1, high = File 2).
2	1A0	Address line for Register File 1 - selects one of 16 words (with 1A1–1A3) using internal 1-of-16 decoder.
3	1A1	Address line for Register File 1 - part of 4-bit address bus for first register file.
4	1A2	Address line for Register File 1 - enables full 16-word addressing within first file.
5	1A3	Address line for Register File 1 - LSB of 4-bit address for Register File 1.
6	1W	Write-enable for Register File 1 - active-low signal enabling data write into selected word of File 1.
7	S2	A-port I/O direction control - low = DQA1–DQA4 outputs, high = inputs (bidirectional bus interface).
8	DQA1	Data I/O for bus A, bit 1 - bidirectional 4-bit port connected to bus A (with DQA2–DQA4).
9	DQA2	Data I/O for bus A, bit 2 - supports simultaneous read/write between A and B buses.
10	DQA3	Data I/O for bus A, bit 3 - used in Multibus-style overlapping register file access.
11	DQA4	Data I/O for bus A, bit 4 - completes 4-bit parallel interface for bus A.
12	GND	Ground reference - common return path for all internal logic and I/O circuits.
13	VCC	Positive supply - powers internal logic, decoders, and 3-state output drivers.
14	S1	File select control - determines which register file connects to bus B (low = File 1, high = File 2).
15	2A3	Address line for Register File 2 - LSB of 4-bit address for second register file.
16	2A2	Address line for Register File 2 - part of independent 4-bit address bus for File 2.
17	2A1	Address line for Register File 2 - enables full 16-word addressing within second file.
18	2A0	Address line for Register File 2 - MSB of 4-bit address for Register File 2.
19	2W	Write-enable for Register File 2 - active-low signal enabling write into selected word of File 2.
20	S3	B-port I/O direction control - low = DQB1–DQB4 outputs, high = inputs (bidirectional bus interface).
21	DQB1	Data I/O for bus B, bit 1 - bidirectional 4-bit port connected to bus B (with DQB2–DQB4).
22	DQB2	Data I/O for bus B, bit 2 - supports dual-bus register exchange without external latches.
23	DQB3	Data I/O for bus B, bit 3 - used in time-critical register file arbitration schemes.
24	DQB4	Data I/O for bus B, bit 4 - completes 4-bit parallel interface for bus B.

Key Features

Feature	Design Value
Dual independent register files	Enables concurrent read/write operations between two 16×4 memory banks - eliminates need for external multiplexing in bus arbitration logic.
Prioritized B-port write control	Hardware-resolved write conflict prevention ensures deterministic behavior when both A and B ports attempt simultaneous writes to same register.
3-state buffer-type outputs	Direct bus-driving capability (24 mA sink) eliminates external bus transceivers in legacy 5-V system designs.
Full port-select and I/O-direction logic	S0–S3 control lines enable eight distinct data routing modes (e.g., A→1R→B, 2R→A + 1R→B) defined in function table - simplifies glue logic in Multibus implementations.
ALS-family speed/power balance	tpd ≤ 26 ns with ICC ≤ 110 mA at VCC = 5.5 V - delivers higher speed than LS logic while maintaining lower power than AS family.

Applications

Industrial PLC Backplane Interface	Multibus-II System Memory Expansion
Use Scenario: Interfacing CPU and I/O modules on a programmable logic controller backplane using standardized 5-V parallel buses. IC Role / Device Role / Timing Role: SN74ALS870NT acts as dual-port register file providing temporary data staging between CPU and peripheral modules, with S2/S3 controlling directionality and S0/S1 selecting active register banks. Use Value: Enables zero-wait-state register-to-register transfers between asynchronous bus domains, reducing cycle time in scan-based control execution.	Use Scenario: Adding local register storage to a Multibus-II expansion card for real-time data buffering during DMA transfers. IC Role / Device Role / Timing Role: SN74ALS870NT serves as overlapping file buffer, allowing CPU to write to one register bank while DMA reads from the other - coordinated via 1W/2W and address lines. Use Value: Eliminates external latch logic and reduces board space by integrating dual 16×4 registers with native bus-drive capability and conflict-free dual-write support.
Legacy Test Equipment Data Acquisition	Real-Time Signal Processing Front-End
Use Scenario: Capturing parallel sensor data in automated test equipment where timing-critical sampling requires minimal latency between capture and processing stages. IC Role / Device Role / Timing Role: SN74ALS870NT functions as synchronized sample-and-hold register, using 1W/2W strobes aligned with ADC conversion completion to store 4-bit channel status or calibration values. Use Value: Provides deterministic 12 ns minimum write pulse width compliance and 15 ns data setup time - ensuring reliable capture at up to 10 MHz sampling rates.	Use Scenario: Implementing coefficient storage and data reordering in fixed-point DSP front-end boards operating under strict 5-V legacy constraints. IC Role / Device Role / Timing Role: SN74ALS870NT operates as dual-configurable lookup table, with S0/S1 selecting filter coefficient sets and S2/S3 toggling between load and execute phases. Use Value: Supports sub-26 ns propagation delay between coefficient update and arithmetic unit input - critical for maintaining pipeline throughput in 16-bit FIR implementations.

Industrial PLC Backplane Interface

Multibus-II System Memory Expansion

Use Scenario: Interfacing CPU and I/O modules on a programmable logic controller backplane using standardized 5-V parallel buses.

IC Role / Device Role / Timing Role: SN74ALS870NT acts as dual-port register file providing temporary data staging between CPU and peripheral modules, with S2/S3 controlling directionality and S0/S1 selecting active register banks.

Use Value: Enables zero-wait-state register-to-register transfers between asynchronous bus domains, reducing cycle time in scan-based control execution.

Use Scenario: Adding local register storage to a Multibus-II expansion card for real-time data buffering during DMA transfers.

IC Role / Device Role / Timing Role: SN74ALS870NT serves as overlapping file buffer, allowing CPU to write to one register bank while DMA reads from the other - coordinated via 1W/2W and address lines.

Use Value: Eliminates external latch logic and reduces board space by integrating dual 16×4 registers with native bus-drive capability and conflict-free dual-write support.

Legacy Test Equipment Data Acquisition

Real-Time Signal Processing Front-End

Use Scenario: Capturing parallel sensor data in automated test equipment where timing-critical sampling requires minimal latency between capture and processing stages.

IC Role / Device Role / Timing Role: SN74ALS870NT functions as synchronized sample-and-hold register, using 1W/2W strobes aligned with ADC conversion completion to store 4-bit channel status or calibration values.

Use Value: Provides deterministic 12 ns minimum write pulse width compliance and 15 ns data setup time - ensuring reliable capture at up to 10 MHz sampling rates.

Use Scenario: Implementing coefficient storage and data reordering in fixed-point DSP front-end boards operating under strict 5-V legacy constraints.

IC Role / Device Role / Timing Role: SN74ALS870NT operates as dual-configurable lookup table, with S0/S1 selecting filter coefficient sets and S2/S3 toggling between load and execute phases.

Use Value: Supports sub-26 ns propagation delay between coefficient update and arithmetic unit input - critical for maintaining pipeline throughput in 16-bit FIR implementations.

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-port register file applications.

Alternative Part	Technical Difference	Application Difference	Selection Advice
SN74AS870N	Faster propagation delay (tpd ≤ 15 ns), higher ICC (150 mA), AS-family process - requires tighter power delivery and heatsinking.	Better suited for high-speed bus arbiters where <15 ns latency is mandatory; not drop-in due to different DC specs and timing margins.	Select SN74AS870N only when SN74ALS870NT's 26 ns tpd is insufficient and board-level thermal design accommodates higher power.
SN74LS870N	Slower speed (tpd ≤ 40 ns), lower drive (IOL = 8 mA), LS-family - reduced noise immunity and bus-loading capability.	Acceptable in low-frequency control systems (<2 MHz bus rate); incompatible with designs requiring 24 mA sink or ALS-level noise rejection.	Choose SN74LS870N only for cost-sensitive, non-critical legacy repairs where SN74ALS870NT availability is constrained and performance margin allows.

Compared with SN74ALS870NT, SN74AS870N offers higher speed at increased power and thermal cost, while SN74LS870N trades performance for lower cost and power - neither is pin-compatible nor functionally identical, and both require validation of timing margins, drive strength, and voltage thresholds in the target system.

Availability

SN74ALS870NT is available at Aetrix Electronics and suitable for industrial PLC backplane interfaces, Multibus-II memory expansion, legacy test equipment data acquisition, real-time signal processing front-ends, and 5-V embedded controller register buffering requiring stable component supply across long-lifecycle programs.

Supply support for SN74ALS870NT includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Texas Instruments is a U.S.-based semiconductor company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.

The SN74ALS870NT belongs to TI's 74ALS advanced low-power Schottky logic family, designed specifically for high-reliability 5-V bus-oriented systems requiring balanced speed, power, and noise immunity - especially in Multibus, VMEbus, and proprietary parallel backplane architectures.

FAQ

What is the maximum clock/data rate supported by SN74ALS870NT?

The SN74ALS870NT does not use a clock signal; it is an asynchronous register file controlled by write-enable pulses and address lines. Its maximum effective data rate is determined by write pulse width (≥12 ns), setup time (≥15 ns), and propagation delay (≤26 ns). In practice, this supports reliable operation up to approximately 10 MHz bus toggle rates when interfaced with compatible 5-V logic families.

Does SN74ALS870NT support true dual-port concurrent read/write operations?

SN74ALS870NT supports overlapping file operations but not simultaneous read and write to the same register location. It allows independent access to two separate 16×4 register banks - e.g., writing to File 1 while reading from File 2 - with S0/S1 controlling file assignment and S2/S3 setting port direction. True dual-port RAM functionality (same address, different ports) is not implemented.

Can SN74ALS870NT be used with modern 3.3-V microcontrollers?

No - SN74ALS870NT is strictly a 5-V device with VIH = 2.0 V min and VIL = 0.8 V max, and its outputs swing rail-to-rail (0 V to VCC). Direct interface with 3.3-V logic requires level-shifting circuitry. The device lacks 3.3-V tolerant inputs or mixed-voltage I/O, and operation below VCC = 4.5 V is outside its recommended conditions.

What is the purpose of the S0–S3 control lines on SN74ALS870NT?

S0 and S1 select which register file (File 1 or File 2) connects to bus A and bus B, respectively. S2 configures DQA1–DQA4 as input or output, and S3 does the same for DQB1–DQB4. Together, these four lines define eight distinct data routing modes - such as "A to 1R, 1R to B" or "2R to A, B to 2R" - as specified in the function table, enabling flexible bus arbitration without external logic.

Is SN74ALS870NT RoHS compliant?

Yes - the SN74ALS870NT variant is Pb-Free (RoHS compliant), with CU NIPDAU lead finish and no exemption required. This is confirmed in TI's official packaging documentation, where SN74ALS870NT is listed under "Pb-Free (RoHS)" eco plan with MSL rating marked "N/A for Pkg Type" due to its PDIP construction.

SN74ALS870NT Specifications

Product attributes: Attribute value

Manufacturer:: Texas Instruments

Series:: 74ALS

Package/Case:: 24-DIP (0.300", 7.62mm)

Packaging:: Tube

Product Status:: Obsolete

Type:: -

Circuit:: -

Independent Circuits:: -

Current - Output High, Low:: -

Voltage Supply Source:: -

Voltage - Supply:: 4.5V ~ 5.5V

Operating Temperature:: 0°C ~ 70°C

Grade:: -

Qualification:: -

Mounting Type:: Through Hole

Supplier Device Package:: 24-PDIP

SN74ALS870NT FAQ

1.How can I place an order for SN74ALS870NT through Aetrix?

Please submit a Request for Quotation (RFQ) for SN74ALS870NT on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.

2.Are the price and stock information for SN74ALS870NT reliable?

The price and inventory of SN74ALS870NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS870NT is usually 5 days.

3.What payment methods are accepted for SN74ALS870NT?

We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS870NT transactions.

Note: Certain payment methods may incur a processing fee.

4.How is shipping managed for SN74ALS870NT?

SN74ALS870NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.

Once your SN74ALS870NT order is processed, you will receive an email with the shipment details and tracking number.

Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.

5.How can I obtain technical support or documentation for SN74ALS870NT?

For technical support, including SN74ALS870NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS870NT requirements.

6.How does Aetrix verify that SN74ALS870NT is sourced from the original manufacturer or authorized distributors?

All SN74ALS870NT products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that SN74ALS870NT meets industry standards.

7.What is the process for return or replacement of SN74ALS870NT?

All SN74ALS870NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS870NT, returns or replacements are accepted under the following conditions:

1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.

2.The issue is reported within 90 days of delivery.

3.The SN74ALS870NT part is unused and in its original packaging.

Return procedure for SN74ALS870NT:

1.Submit a request within 90 days.

2.Obtain a Return Material Authorization (RMA) from Aetrix.

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