My Inquiry
My Account
Texas Instruments SN74ALS870DWR
- Part No.:
- SN74ALS870DWR
- Manufacturer:
- Texas Instruments
- Category:
- Signal Switches, Multiplexers, Decoders
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS870DWR.pdf
- Description:
- IC REGISTER FILE DL 16X4 24-SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,125
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
SN74ALS870DWR from Texas Instruments is a dual 16-word × 4-bit register file IC with independent write-enable controls (1W, 2W), four-bit bidirectional I/O ports (DQA1–DQA4 and DQB1–DQB4), 3-state buffer-type outputs, and priority-controlled dual-input bus arbitration for Multibus-compatible systems. It operates from 0°C to 70°C with VCC = 4.5–5.5 V and supports overlapping register file operations in industrial control and legacy bus-based computing.
For engineers reviewing the SN74ALS870DWR datasheet, SN74ALS870DWR pinout, SN74ALS870DWR application, or SN74ALS870DWR equivalent, key selection criteria include its 24-pin SOIC-DW package, 16×4 register depth per file, S0–S3 select logic for port routing, 24 mA low-level output drive, and dual-port conflict resolution via B-input priority - all critical for retro-computing, bus interface design, and register-intensive embedded controllers.
Technical Context
The SN74ALS870DWR integrates two independent 16×4 RAM arrays with internal 1-of-16 address decoders driven by 1A0–1A3 or 2A0–2A3 inputs. Each file has dedicated write-enable (1W/2W) and separate address buses, enabling concurrent access control.
S0/S1 select which register file connects to each data port; S2/S3 configure A- and B-port direction (input/output); and the prioritized B-input path prevents write collisions during dual-input mode - a deterministic hardware arbitration mechanism essential for Multibus II timing compliance.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Function | Dual 16-word × 4-bit register file with independent write enables and bidirectional I/O ports |
| Supply Voltage | 4.5 V to 5.5 V - compatible with standard 5 V TTL/ALS logic rails and legacy power domains |
| Output Drive | 24 mA sink capability - sufficient to directly drive terminated Multibus or backplane traces without external buffers |
| Propagation Delay | 5 ns to 26 ns (CL = 50 pF) - ensures sub-40 MHz bus operation with setup/hold margin for asynchronous writes |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial control and desktop computing environments |
| Input Thresholds | VIL = 0.8 V, VIH = 2.0 V - ALS-family TTL-compatible logic levels with noise immunity for noisy bus environments |
| 3-State Enable Time | 3 ns to 17 ns - fast output enable/disable supports dynamic bus sharing in time-multiplexed architectures |
Pinout & Package
SN74ALS870DWR is housed in a 24-pin SOIC (DW) package measuring 7.5 mm × 15.4 mm with 0.65 mm lead pitch and RoHS-compliant CU NIPDAU finish (MSL Level-1).
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | S0 | File select control: determines which register file connects to port A/B in combination with S1 |
| 2 | 1A0 | Address line 0 for register file 1 - selects one of 16 words in first 4-bit register array |
| 3 | 1A1 | Address line 1 for register file 1 - part of 4-bit address bus decoding 16 locations |
| 4 | 1A2 | Address line 2 for register file 1 - enables full word addressing without external decoder logic |
| 5 | 1A3 | Address line 3 for register file 1 - completes 16-word address space for first register file |
| 6 | 1W | Write-enable for register file 1 - active-low signal enabling data capture on rising edge of write pulse |
| 7 | S2 | A-port I/O direction control - high = input, low = output (configures DQA1–DQA4 as bus driver or receiver) |
| 8 | DQA1 | Data I/O bit 1 for port A - bidirectional 4-bit bus interface supporting read/write cycles on bus A |
| 9 | DQA2 | Data I/O bit 2 for port A - synchronized with S2 to support simultaneous 4-bit transfers |
| 10 | DQA3 | Data I/O bit 3 for port A - enables full parallel data movement between CPU and register file |
| 11 | DQA4 | Data I/O bit 4 for port A - completes 4-bit port A interface for register file 1 or 2 depending on S0/S1 |
| 12 | GND | Ground reference - common return for all logic and I/O circuits; requires low-impedance PCB connection |
| 13 | VCC | Positive supply - powers internal logic, decoders, and 3-state output drivers at 4.5–5.5 V |
| 14 | S1 | File select control: works with S0 to route either register file to A or B port per function table |
| 15 | 2A3 | Address line 3 for register file 2 - selects word in second 16×4 register array independently of file 1 |
| 16 | 2A2 | Address line 2 for register file 2 - supports concurrent addressing of both files for overlapping operations |
| 17 | 2A1 | Address line 1 for register file 2 - enables independent access without bus contention |
| 18 | 2A0 | Address line 0 for register file 2 - provides full 16-word addressability for second register bank |
| 19 | 2W | Write-enable for register file 2 - active-low control allowing selective write to second file while first remains static |
| 20 | S3 | B-port I/O direction control - high = input, low = output (configures DQB1–DQB4 for bus B interaction) |
| 21 | DQB1 | Data I/O bit 1 for port B - bidirectional interface supporting independent read/write on bus B |
| 22 | DQB2 | Data I/O bit 2 for port B - enables full 4-bit parallel transfer on secondary bus segment |
| 23 | DQB3 | Data I/O bit 3 for port B - supports register-to-register transfers across A and B ports |
| 24 | DQB4 | Data I/O bit 4 for port B - completes 4-bit port B interface with priority arbitration over A-port writes |
Key Features
| Feature | Design Value |
|---|---|
| Dual independent 16×4 register files | Enables simultaneous storage and retrieval from two logically separate memory banks without shared address/data conflicts |
| Prioritized B-input port arbitration | Hardware-resolved write conflict prevention during dual-input mode - eliminates need for external bus grant logic |
| 3-state buffer-type outputs | Direct bus-line driving capability with 24 mA sink current - removes requirement for external line drivers in Multibus designs |
| Individual write-enable and address lines per file | Supports overlapping file operations and asynchronous updates - critical for real-time register shadowing and pipeline buffering |
| S0–S3 select logic with full function table | Eight configurable I/O routing modes including A→1R→B, A→2R→B, B→1R, and B→2R - enables flexible data path mapping |
Applications
| Legacy Multibus Systems | Industrial PLC Register Banks |
|---|---|
Use Scenario: Replacing aging discrete TTL register stacks in DEC LSI-11 or Motorola MVME-series backplanes requiring compact, reliable 16-word storage per channel. IC Role / Device Role / Timing Role: Dual register file acting as addressable scratchpad memory with deterministic bus arbitration and cycle-accurate write enable timing. Use Value: Reduces board space by >70% vs. discrete 74ALS170 implementations while maintaining full Multibus II electrical and timing compatibility. |
Use Scenario: Providing isolated 4-bit I/O register sets in programmable logic controller I/O modules where deterministic read-modify-write sequences are required across multiple sensor/actuator channels. IC Role / Device Role / Timing Role: Dual-port register file serving as hardware-accelerated status/control latch with independent write enables per channel. Use Value: Enables atomic 4-bit updates without software masking, eliminating race conditions during concurrent ladder logic scan cycles. |
| Retrocomputing Memory Expansion | Bus Interface Protocol Translation |
Use Scenario: Adding expandable register space to Z80 or 68000-based hobbyist computers using ISA-like or custom backplanes with 5 V TTL signaling. IC Role / Device Role / Timing Role: Configurable register file mapped into I/O space, supporting both memory-mapped and port-mapped access via S0–S3 control. Use Value: Provides 32 words of fast, low-latency storage (16 per file) with no wait states - ideal for video frame buffers or interrupt vector tables. |
Use Scenario: Bridging mismatched data widths between 4-bit peripheral controllers (e.g., keypad encoders) and 8/16-bit system buses in embedded instrumentation. IC Role / Device Role / Timing Role: Bidirectional 4-bit register file acting as synchronous protocol adapter with direction-controlled I/O ports (S2/S3). Use Value: Eliminates glue logic by absorbing width conversion, handshaking, and bus isolation - reduces BOM count and layout complexity. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar dual-register-file applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74AS870DWR | Faster propagation delay (typ. 6 ns vs. 12 ns), higher ICC (130 mA), AS-family voltage thresholds (VIH = 2.0 V, VIL = 0.5 V) | Requires tighter power delivery and lower-noise layout; suitable only where speed justifies increased power and cost | Select SN74AS870DWR only when sub-20 ns tpd is mandatory and thermal/power budgets allow +20% ICC increase. |
| SN74LS870N | Same pinout but PDIP-24 (NT) package; LS-family logic thresholds (VIH = 2.0 V, VIL = 0.8 V); slower tpd (max 40 ns); higher VOL (0.5 V) | Limited to through-hole prototyping or legacy repair; not suitable for high-density SOIC layouts or >25 MHz bus operation | Choose SN74LS870N only for hand-soldered repairs or educational labs where SOIC rework is impractical. |
Compared with SN74AS870DWR, the SN74ALS870DWR offers better noise immunity and lower power at moderate speed; compared with SN74LS870N, it delivers superior timing performance and SOIC packaging for modern PCB assembly - making it the optimal balance for industrial retro-designs requiring reliability, density, and bus compatibility.
Availability
SN74ALS870DWR is available at Aetrix Electronics and suitable for legacy system repair, industrial PLC upgrades, and retrocomputing projects requiring stable component supply with long-term traceability and RoHS-compliant manufacturing.
Supply support for SN74ALS870DWR 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 innovator founded in 1930, specializing in analog, logic, and embedded processing technologies with broad industrial and automotive reach.
The SN74ALS870DWR belongs to TI's 74ALS advanced low-power Schottky logic family, designed specifically for high-reliability, bus-oriented register storage in Multibus, VMEbus, and proprietary backplane architectures of the 1980s–1990s.
FAQ
What is the maximum clock frequency supported by SN74ALS870DWR?
The SN74ALS870DWR does not contain an internal clock; it is an asynchronous register file. Its maximum effective bus frequency depends on external write pulse width (min 12 ns) and propagation delays (5–26 ns). For reliable operation with setup/hold margins, it supports up to ~25 MHz bus cycles in typical Multibus configurations with proper termination and layout.
Does SN74ALS870DWR support hot-swapping or live insertion?
No, the SN74ALS870DWR is not designed for hot-swapping. Its absolute maximum ratings specify no exposure to powered insertion - VCC must be stable before applying input signals, and all pins must remain within VI limits (–0.5 V to 7 V) during power-up/down. Use sequenced power supplies and input clamping if integration into hot-plug systems is required.
Can SN74ALS870DWR operate with a 3.3 V supply?
No, the SN74ALS870DWR requires a minimum VCC of 4.5 V and is specified only for 4.5–5.5 V operation. Applying 3.3 V will result in undefined logic states, insufficient output drive, and potential failure to meet VIH/VIL thresholds. It is incompatible with mixed-voltage 3.3 V/5 V systems without level translation.
How does the B-input priority feature prevent write conflicts in SN74ALS870DWR?
In dual-input mode (e.g., S0=H, S1=L, S2=H, S3=H), both A and B ports attempt to write to the same register file. The SN74ALS870DWR hardware gives unconditional priority to B-port writes: if 2W is asserted while 1W is also active, only the B-port data is latched. This eliminates bus arbitration logic and guarantees deterministic behavior without software intervention.
Is SN74ALS870DWR pin-compatible with SN74ALS873 or SN74ALS871?
No, SN74ALS870DWR is not pin-compatible with SN74ALS873 or SN74ALS871. The SN74ALS873 is a 16×4 FIFO with different pin functions (e.g., RCLK, WCLK, EMPTY, FULL), and the SN74ALS871 is a 16×4 dual-port RAM with distinct control signal mapping (e.g., OE, CE). Pin counts and signal assignments differ fundamentally - direct replacement is not possible.
SN74ALS870DWR Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- 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
SN74ALS870DWR FAQ
1.How can I place an order for SN74ALS870DWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS870DWR 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 SN74ALS870DWR reliable?
The price and inventory of SN74ALS870DWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS870DWR is usually 5 days.
3.What payment methods are accepted for SN74ALS870DWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS870DWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS870DWR?
SN74ALS870DWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS870DWR 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 SN74ALS870DWR?
For technical support, including SN74ALS870DWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS870DWR requirements.
6.How does Aetrix verify that SN74ALS870DWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS870DWR 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 SN74ALS870DWR meets industry standards.
7.What is the process for return or replacement of SN74ALS870DWR?
All SN74ALS870DWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS870DWR, 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 SN74ALS870DWR part is unused and in its original packaging.
Return procedure for SN74ALS870DWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
SN74ALS870DWR Tags
-
SN74HC138DR
Texas Instruments
-
TC7SB3157CFU,LF(CT
Toshiba Semiconductor and Storage
-
74CBTLV3257PW,118
Nexperia USA Inc.
-
SN74CBTLV3257PWR
Texas Instruments
-
74CBTLV3257GUX
Nexperia USA Inc.
-
74HC154BQ,118
Nexperia USA Inc.
-
P3S0200GMX
NXP USA Inc.
-
SN74CB3Q3245PWR
Texas Instruments
-
SN74CB3Q3257RGYR
Texas Instruments
-
TCA9543APWR
Texas Instruments
-
TCA9546APWR
Texas Instruments
-
SN74HC138N
Texas Instruments
Tech Hub
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
An engineering guide to LED driver operation, constant-current and constant-voltage outputs, linear and switching topologies, dimming, IC selection, calculations, replacement compatibility, and fault c…
Operational amplifier guide covering op amp basics, feedback, ideal vs real op amps, common configurations, buffer circuits, offset, bias current, gain-bandwidth, slew rate, rail-to-rail limits and sel…
Jumper cables guide covering safe connection order, red and black clamp placement, final ground connection, cable gauge, length, clamp quality, copper vs CCA cables, jump starter comparison and battery…
