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Texas Instruments SN74ALS870DW
- Part No.:
- SN74ALS870DW
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS870DW.pdf
- Description:
- IC REGISTER FILE DL 16X4 24-SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,025
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Product details
Overview
SN74ALS870DW from Texas Instruments is a dual 16-word × 4-bit register file IC with 3-state buffer-type outputs, individual write-enable controls (1W/2W), independent address decoding (1A0–1A3 and 2A0–2A3), and dual 4-bit I/O ports (DQA1–DQA4 and DQB1–DQB4) designed for direct bus-line driving in Multibus-compatible systems.
For engineers reviewing the SN74ALS870DW datasheet, SN74ALS870DW pinout, SN74ALS870DW application, or SN74ALS870DW equivalent, key selection considerations include its 24-pin SOIC (DW) package, ALS logic family timing (tpd ≤ 26 ns), 0°C to 70°C operating range, 5 V supply compatibility, and dual-register file architecture enabling overlapping read/write operations between bus A and bus B.
Technical Context
The SN74ALS870DW implements two independent 16×4 RAM arrays with separate address buses and write enables, supporting simultaneous access control via S0/S1 file select lines and S2/S3 I/O direction controls. Its internal 1-of-16 decoders route addresses to selected register words without external logic.
Priority arbitration resolves dual-input conflicts by giving precedence to the B-input port during concurrent writes. All outputs are 3-state buffers rated for 24 mA sink current and –2.6 mA source current, meeting ALS family drive requirements for TTL-compatible bus loading.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Dual 16-word × 4-bit register file with independent write enable and address decode |
| Logic Family | Advanced Low-Power Schottky (ALS), compatible with TTL input thresholds |
| Supply Voltage | 4.5 V to 5.5 V - ensures stable operation across standard 5 V rail tolerances |
| Propagation Delay | ≤ 26 ns (DQA ↔ DQB) - supports high-speed bus handshaking in legacy computing systems |
| Output Drive | 24 mA sink / –2.6 mA source - directly drives multiple TTL loads without external buffers |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade embedded and industrial control applications |
| I/O Configuration | Two 4-bit bidirectional ports (DQA/DQB) with programmable input/output direction per port |
Pinout & Package
SN74ALS870DW uses a 24-pin SOIC (DW) package with 300-mil body width, RoHS-compliant green finish (CU NIPDAU), and moisture sensitivity level (MSL) 1 rating for unlimited floor life at 260°C reflow.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1A0–1A3 | Address inputs for Register File 1 | Select one of 16 words in first 4-bit register file; decoded internally |
| 2A0–2A3 | Address inputs for Register File 2 | Select one of 16 words in second 4-bit register file; independent decode path |
| DQA1–DQA4 | Data I/O port A | Bidirectional 4-bit interface to Bus A; direction controlled by S2 |
| DQB1–DQB4 | Data I/O port B | Bidirectional 4-bit interface to Bus B; direction controlled by S3 |
| S0, S1 | Register file select | Configure which register file connects to each bus (e.g., S0=L/S1=L → 1R to A, 1R to B) |
| S2, S3 | I/O direction control | S2 sets DQA port direction (input/output); S3 sets DQB port direction |
| 1W, 2W | Write enable for Register Files 1 and 2 | Active-low enables write to respective register file; independent control prevents bus contention |
| VCC, GND | Power supply terminals | Single 5 V supply with dedicated ground; decoupling required per ALS design practice |
Key Features
| Feature | Design Value |
|---|---|
| Dual register file architecture | Enables concurrent read/write operations between Bus A and Bus B without external arbitration logic |
| Prioritized B-input port | Resolves write conflicts automatically during dual-input mode, eliminating need for external priority encoder |
| Individual write-enable controls | Allows selective updating of either register file while the other remains transparent or holds state |
| 3-state buffer outputs | Directly interfaces with shared data buses without external line drivers or pull-ups |
| Multibus architecture support | Designed specifically for overlapping file operations in legacy computer and controller backplane systems |
Applications
| Industrial PLC Backplanes | Legacy Computer System Expansion |
|---|---|
Use Scenario: Interfacing multiple I/O modules to a central processor over a shared parallel bus in programmable logic controllers. IC Role / Device Role / Timing Role: Dual register file acts as configurable data staging buffer between CPU and peripheral modules, enabling non-blocking register access. Use Value: Eliminates software wait states during overlapping reads/writes across bus A and bus B, improving scan cycle throughput. | Use Scenario: Adding memory-mapped peripheral registers to vintage minicomputer systems using Multibus-compatible expansion slots. IC Role / Device Role / Timing Role: Provides two independent 16×4 register banks mapped to distinct address ranges, accessible via standard bus protocol. Use Value: Reduces board-level gate count by integrating address decoding and 3-state bus drivers into a single 24-pin IC. |
| Real-Time Data Acquisition Systems | Embedded Control State Machines |
Use Scenario: Capturing synchronized sensor samples from two independent analog front-ends before batch transfer to host processor. IC Role / Device Role / Timing Role: Registers act as dual-port FIFO-like storage: one port accepts ADC data (B-input priority), second port streams to host (A-output). Use Value: Prevents sample loss during host read cycles due to built-in write conflict resolution and independent write enables. | Use Scenario: Implementing finite-state machine register sets in fixed-function industrial controllers where state variables must be updated asynchronously. IC Role / Device Role / Timing Role: Stores current and next state vectors in separate register files, allowing atomic state transitions via S0/S1-controlled routing. Use Value: Enables glitch-free state updates without requiring external latches or clock-domain crossing logic. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-register-file applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AS870DW | Faster propagation delay (≤ 12 ns), higher ICC (140 mA), AS logic family - requires tighter power delivery | Better suited for high-speed bus timing-critical designs but less tolerant of marginal VCC or temperature | Choose when tpd < 15 ns is mandatory and power budget allows +30% increase |
| SN74LS870N | Same pinout and function but in PDIP (NT) package; slower speed (tpd ≤ 35 ns); LS logic family | Compatible with through-hole prototyping and legacy socketed systems; lower drive strength (8 mA sink) | Choose for hand-soldered development boards or replacement in existing LS-based systems |
Compared with SN74ALS870DW, SN74AS870DW delivers higher speed at increased power cost, while SN74LS870N offers drop-in mechanical compatibility with reduced performance - making SN74ALS870DW the optimal balance of speed, drive capability, and power efficiency in SOIC-based designs.
Availability
SN74ALS870DW is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer system expansion, and real-time data acquisition systems requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS870DW 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 global semiconductor company headquartered in Dallas, Texas, delivering analog and embedded processing solutions across industrial, automotive, and communications markets.
The SN74ALS870DW belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power register file and bus-interface functions in early microcomputer and industrial control architectures.
FAQ
What is the maximum clock frequency supported by SN74ALS870DW?
The SN74ALS870DW does not contain an internal clock; it is a synchronous register file controlled by external write strobes. Its minimum write pulse width (tw) is 12 ns, supporting effective operation up to approximately 40 MHz in systems with appropriate setup/hold timing margins. Timing depends on external address and control signal synchronization rather than a dedicated clock input.
Does SN74ALS870DW support hot-swapping or live insertion?
No, SN74ALS870DW is not designed for hot-swapping. Its absolute maximum ratings specify that all inputs must remain within –0.5 V to VCC + 0.5 V during operation, and no protection circuitry is provided for live insertion transients. Power sequencing and static discharge precautions are required before board insertion or removal.
Can SN74ALS870DW operate with a 3.3 V supply?
No, SN74ALS870DW requires a minimum supply voltage of 4.5 V and is specified only for 4.5 V to 5.5 V operation. Applying 3.3 V will result in undefined logic levels, insufficient output drive, and potential failure to meet VIH/VIL thresholds - it is incompatible with 3.3 V logic families without level translation.
How does the priority arbitration work between DQA and DQB ports on SN74ALS870DW?
During dual-input mode (e.g., S0=H/S1=L and S2=H/S3=H), the B-input port (DQB1–DQB4) takes priority over the A-input port. If both ports attempt to write to the same register word simultaneously, the B-port data is latched and the A-port write is ignored - preventing bus contention without external logic.
Is SN74ALS870DW pin-compatible with SN74ALS870N?
Yes, SN74ALS870DW and SN74ALS870N share identical pin functions and ordering, differing only in package type: DW is 24-pin SOIC, NT is 24-pin PDIP. Signal mapping, electrical behavior, and timing specifications are identical - enabling direct PCB footprint substitution where package height and soldering method permit.
SN74ALS870DW Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- 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:
- Surface Mount
- Supplier Device Package:
- 24-SOIC
SN74ALS870DW FAQ
1.How can I place an order for SN74ALS870DW through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS870DW 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 SN74ALS870DW reliable?
The price and inventory of SN74ALS870DW are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS870DW is usually 5 days.
3.What payment methods are accepted for SN74ALS870DW?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS870DW transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS870DW?
SN74ALS870DW orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS870DW 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 SN74ALS870DW?
For technical support, including SN74ALS870DW datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS870DW requirements.
6.How does Aetrix verify that SN74ALS870DW is sourced from the original manufacturer or authorized distributors?
All SN74ALS870DW 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 SN74ALS870DW meets industry standards.
7.What is the process for return or replacement of SN74ALS870DW?
All SN74ALS870DW units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS870DW, 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 SN74ALS870DW part is unused and in its original packaging.
Return procedure for SN74ALS870DW:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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