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Texas Instruments SN74ALS621ADWRG4
- Part No.:
- SN74ALS621ADWRG4
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS621ADWRG4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:2,881
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Product details
Overview
SN74ALS621ADWRG4 from Texas Instruments is an octal bus transceiver with open-collector outputs and true logic polarity, designed for asynchronous bidirectional data transfer between A and B buses in TTL-compatible systems. It operates from 4.5 V to 5.5 V, supports 0°C to 70°C ambient, delivers 24 mA low-level output current (48 mA in -1 version), and features dual output-enable inputs (OEAB/OEBA) enabling bus isolation or latch-mode operation.
For engineers reviewing the SN74ALS621ADWRG4 datasheet, SN74ALS621ADWRG4 pinout, SN74ALS621ADWRG4 application, or SN74ALS621ADWRG4 equivalent, this device is selected for legacy industrial backplane interfaces, memory-mapped I/O expansion, and bidirectional address/data multiplexing where open-collector drive and bus-hold capability are required.
Technical Context
The SN74ALS621ADWRG4 implements a dual-bus transceiver architecture with independent OEAB (A-to-B enable) and OEBA (B-to-A enable) controls, allowing simultaneous bidirectional communication or high-impedance isolation of both buses. Its open-collector outputs require external pull-up resistors and support wired-AND logic implementation.
When both OEAB and OEBA are asserted, the device enters local bus-latch mode: outputs reinforce their inputs, preserving bus states across both A and B sides while all other drivers are tri-stated - enabling transparent data storage without additional latches.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Type | True (non-inverting) data path - preserves signal polarity during A↔B transfer |
| Output Configuration | Open-collector - enables wired-AND bus sharing and level translation via external pull-ups |
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL supply rails and noise margin requirements |
| IOL (Standard) | 24 mA - sufficient to drive multiple TTL loads or 50 Ω transmission lines under terminated conditions |
| Propagation Delay | 5 ns to 20 ns (A↔B) - ensures timing compliance in sub-25 MHz synchronous bus systems |
| Operating Temperature | 0°C to 70°C - qualified for commercial-grade industrial control and instrumentation environments |
| Package | SOIC-20 (DW) - surface-mount footprint with 1.27 mm pitch, 7.5 mm width, and 2.65 mm max height |
Pinout & Package
SN74ALS621ADWRG4 is housed in a 20-pin SOIC (DW) package per JEDEC MS-013, with 1.27 mm lead pitch, 7.5 mm body width, and 2.65 mm maximum height. Pin 1 is located at the top-left corner with notch or index mark indication.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OEAB) | A-to-B Output Enable | Active-low control: enables A-port drivers to drive B bus when low; disables A outputs when high |
| 2–9 (A1–A8) | Input/Output Port A | Open-collector bidirectional data lines connected to A-side bus; require external pull-up |
| 10 (GND) | Ground Reference | Power return path for internal logic and output stages; must be low-inductance connection |
| 11–18 (B1–B8) | Input/Output Port B | Open-collector bidirectional data lines connected to B-side bus; electrically isolated from A when OEs inactive |
| 19 (OEBA) | B-to-A Output Enable | Active-low control: enables B-port drivers to drive A bus when low; disables B outputs when high |
| 20 (VCC) | Positive Supply | 5 V nominal power rail; decoupling capacitor (0.1 µF) required within 10 mm of pin |
Key Features
| Feature | Design Value |
|---|---|
| Local Bus-Latch Capability | Simultaneous assertion of OEAB and OEBA holds last valid state on both A and B buses without external latches |
| True Logic Polarity | Non-inverting data path simplifies system-level signal integrity analysis and eliminates need for inversion compensation |
| Dual Independent Enables | OEAB and OEBA allow asymmetric bus control - e.g., A→B only, B→A only, or full isolation - enabling flexible protocol timing |
| Open-Collector Outputs | Supports wired-AND arbitration, multi-drop bus topologies, and voltage-level translation via selectable pull-up voltage |
| TTL-Compatible Interface | Meets ALS-family input thresholds (VIH = 2 V, VIL = 0.8 V) and output drive specs for seamless integration into legacy 5 V systems |
Applications
| Industrial Backplane Interface | Memory-Mapped I/O Expansion |
|---|---|
Use Scenario: Bidirectional data exchange between CPU bus and peripheral slots in modular PLC chassis using shared backplane wiring. IC Role / Device Role / Timing Role: SN74ALS621ADWRG4 acts as a direction-controlled bus buffer, isolating CPU and peripheral address/data lines while supporting hot-swap-safe enable sequencing. Use Value: Open-collector outputs prevent bus contention during insertion/removal; latch mode retains slot configuration during reset sequences. |
Use Scenario: Expanding microcontroller GPIO count by connecting parallel I/O ports (e.g., 8-bit port expander) to main data bus. IC Role / Device Role / Timing Role: SN74ALS621ADWRG4 serves as a bidirectional data path between MCU D0–D7 and peripheral I/O register, controlled by address-decoded OE signals. Use Value: True logic preserves register read/write polarity; 24 mA drive supports direct connection to multiple CMOS/TTL inputs without buffers. |
| Legacy System Bus Arbitration | Address/Data Multiplexing |
Use Scenario: Implementing priority-based bus arbitration in multi-master 8-bit systems using wired-AND request lines. IC Role / Device Role / Timing Role: SN74ALS621ADWRG4 provides open-collector drivers for BUSRQ/BUSAK handshake signals, enabling hardware-level grant resolution. Use Value: Wired-AND capability allows multiple masters to share single request line; propagation delay ≤20 ns ensures deterministic arbitration timing. |
Use Scenario: Demultiplexing shared address/data bus in Z80- or 8085-based designs where AD0–AD7 carry both address LSBs and data. IC Role / Device Role / Timing Role: SN74ALS621ADWRG4 buffers ADx lines between CPU and memory/peripheral chips, enabled by ALE or RD/WR strobes. Use Value: Dual-OE control permits precise timing alignment with CPU control signals; latch mode holds address during memory access cycles. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS623ADW | 3-state (not open-collector) outputs, true logic, same pinout and timing | Requires separate bus drivers for wired-AND; unsuitable for multi-drop arbitration or level translation | Select when bus isolation without external pull-ups is preferred and contention-free driving is guaranteed |
| SN74AS623DW | Faster propagation (1–9 ns), higher IOL (64 mA), AS-family speed grade, same pinout | Higher power consumption (ICC up to 189 mA); may require thermal derating in dense layouts | Select for high-speed backplanes (>25 MHz) where ALS timing margins are insufficient |
Compared with SN74ALS621ADWRG4, SN74ALS623ADW trades open-collector flexibility for simpler 3-state control, while SN74AS623DW delivers 2× speed at the cost of 4× quiescent current - making SN74ALS621ADWRG4 optimal for power-constrained, wired-AND–dependent legacy interfaces.
Availability
SN74ALS621ADWRG4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, memory-mapped I/O expansion, legacy system bus arbitration, and address/data multiplexing requiring stable component supply across long-life embedded programs.
Supply support for SN74ALS621ADWRG4 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 leader with over 90 years of analog and logic innovation, delivering reliable, high-performance components for industrial, automotive, and communications infrastructure.
The SN74ALS621ADWRG4 belongs to TI's legacy ALS (Advanced Low-Power Schottky) logic family, engineered for robust 5 V TTL interoperability, low static power, and predictable timing in mission-critical industrial control systems.
FAQ
What is the output configuration of the SN74ALS621ADWRG4?
The SN74ALS621ADWRG4 features open-collector outputs on both A and B ports, requiring external pull-up resistors for proper logic high levels. This configuration supports wired-AND bus sharing, multi-drop topologies, and voltage-level translation - a key differentiator from 3-state alternatives like SN74ALS623ADW. The SN74ALS621ADWRG4 does not provide internal pull-ups or active-high outputs.
Does the SN74ALS621ADWRG4 support bus-latch functionality?
Yes, the SN74ALS621ADWRG4 supports local bus-latch mode when both OEAB and OEBA are asserted low. In this state, each output reinforces its corresponding input, maintaining the last valid logic state on both A and B buses while all other drivers are tri-stated. This eliminates the need for external latches in applications like configuration retention during processor reset - a feature confirmed in the SDAS226A datasheet function description.
What is the maximum low-level output current rating for the SN74ALS621ADWRG4?
The standard SN74ALS621ADWRG4 is rated for 24 mA low-level output current (IOL) per pin under recommended operating conditions (VCC = 4.5 V, TA = 0°C to 70°C). The -1 variant (e.g., SN74ALS621A-1N) increases this to 48 mA, but SN74ALS621ADWRG4 is the standard version and does not include the -1 suffix - therefore its validated IOL remains 24 mA, as specified in Section 4 of the SDAS226A datasheet.
Is the SN74ALS621ADWRG4 pin-compatible with other devices in the SN74ALS62x family?
Yes, the SN74ALS621ADWRG4 shares identical SOIC-20 (DW) pinout and terminal assignments with SN74ALS620ADW, SN74ALS623ADW, and SN74AS623DW - including OEAB, OEBA, A1–A8, B1–B8, VCC, and GND locations. However, functional differences exist: SN74ALS620A is inverting, SN74ALS623A uses 3-state outputs, and SN74AS623 offers faster timing. Direct substitution requires verification of logic polarity and output type.
What temperature range is the SN74ALS621ADWRG4 qualified for?
The SN74ALS621ADWRG4 is characterized and qualified for operation from 0°C to 70°C ambient temperature, consistent with commercial-grade TTL logic specifications. This range is explicitly stated in the "Recommended Operating Conditions" table for SN74ALS621A on page 5 of the SDAS226A datasheet and applies to all package variants including the DW (SOIC) and RG4-marked tape-and-reel format.
SN74ALS621ADWRG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- Open Collector
- Current - Output High, Low:
- -, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 20-SOIC
SN74ALS621ADWRG4 FAQ
1.How can I place an order for SN74ALS621ADWRG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621ADWRG4 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 SN74ALS621ADWRG4 reliable?
The price and inventory of SN74ALS621ADWRG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621ADWRG4 is usually 5 days.
3.What payment methods are accepted for SN74ALS621ADWRG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS621ADWRG4 transactions.
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4.How is shipping managed for SN74ALS621ADWRG4?
SN74ALS621ADWRG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS621ADWRG4 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 SN74ALS621ADWRG4?
For technical support, including SN74ALS621ADWRG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621ADWRG4 requirements.
6.How does Aetrix verify that SN74ALS621ADWRG4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS621ADWRG4 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 SN74ALS621ADWRG4 meets industry standards.
7.What is the process for return or replacement of SN74ALS621ADWRG4?
All SN74ALS621ADWRG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621ADWRG4, 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 SN74ALS621ADWRG4 part is unused and in its original packaging.
Return procedure for SN74ALS621ADWRG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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