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Texas Instruments SN74ALS621ADWR
- Part No.:
- SN74ALS621ADWR
- Manufacturer:
- Texas Instruments
- Package:
- 20-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
SN74ALS621ADWR.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:1,759
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Product details
Overview
SN74ALS621ADWR 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-level systems. It supports 5 V operation, delivers 24 mA low-level output current (48 mA in -1 variant), operates from 0°C to 70°C, and features dual output-enable controls (OEAB/OEBA) enabling bus-latch functionality in isolated configurations.
For engineers reviewing the SN74ALS621ADWR datasheet, SN74ALS621ADWR pinout, SN74ALS621ADWR application, or SN74ALS621ADWR equivalent, this device is selected for legacy industrial backplane interfaces, bidirectional memory/data bus isolation, and TTL-compatible level-shifting where open-collector drive and bus-hold capability are required.
Technical Context
The SN74ALS621ADWR implements a dual-enable octal transceiver architecture with independent OEAB (A-to-B enable) and OEBA (B-to-A enable) inputs, allowing flexible direction control and simultaneous bus latching when both enables are active. Its open-collector outputs require external pull-ups and support wired-AND logic implementation.
It belongs to the ALS (Advanced Low-Power Schottky) family, offering improved speed-power trade-offs over standard LS logic, with propagation delays as low as 5 ns (tPHL, B→A) and disable times under 12 ns (tPZL, OEBA→A). All I/O pins tolerate 5.5 V, and absolute maximum ratings include 7 V supply and input voltage limits.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Family | ALS (Advanced Low-Power Schottky) - ensures TTL compatibility with reduced power vs. standard LS, suitable for legacy 5 V systems. |
| Output Type | Open-collector - requires external pull-up resistors; enables wired-AND bus sharing and level translation across different voltage domains. |
| Supply Voltage | 4.5 V to 5.5 V - tightly regulated 5 V operation; not rated for 3.3 V or mixed-voltage use. |
| Output Drive | 24 mA (IOL, standard); 48 mA (IOL, -1 variant) - sufficient for driving multiple TTL loads or longer traces in industrial backplanes. |
| Propagation Delay | 5–33 ns (tPHL/tPLH, A↔B) - meets timing requirements for sub-20 MHz asynchronous bus handshaking in control-plane applications. |
| Operating Temperature | 0°C to 70°C - commercial-grade rating; validated for indoor industrial enclosures and non-extended-environment embedded systems. |
| Package | SOIC-20 (DW) - 0.3" wide, 1.27 mm pitch, 2.65 mm max height; compatible with standard surface-mount reflow profiles (MSL Level-1). |
Pinout & Package
SN74ALS621ADWR is housed in a 20-pin SOIC (DW) package with 1.27 mm lead pitch and 7.6 mm body width. Pin 1 is located at the top-left corner (notch-side indicator), with pins numbered counter-clockwise.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OEAB) | A-to-B Output Enable | Active-low control: asserts A→B data path when low; high-Z isolates A bus from B bus. |
| 2–9 (A1–A8) | Input/Output Port A | Open-collector bidirectional I/O lines tied to A-side bus; require external pull-up for logic HIGH. |
| 10 (GND) | Ground Reference | Primary signal return path; must be low-inductance connection to minimize noise coupling in bus switching. |
| 11–18 (B1–B8) | Input/Output Port B | Open-collector bidirectional I/O lines tied to B-side bus; electrically identical to A port behavior. |
| 19 (OEBA) | B-to-A Output Enable | Active-low control: asserts B→A data path when low; high-Z isolates B bus from A bus. |
| 20 (VCC) | Power Supply | +5 V DC supply; bypassing with 0.1 µF ceramic capacitor near pin is mandatory for stable switching performance. |
Key Features
| Feature | Design Value |
|---|---|
| True Logic Polarity | Non-inverting data transfer (A↔B) - preserves signal phase integrity in control-path monitoring and diagnostic loops. |
| Dual Output-Enable Control | Independent OEAB and OEBA inputs - enables selective unidirectional flow, full isolation, or simultaneous bus latching without external logic. |
| Bus-Latch Capability | Both OEAB and OEBA asserted → ports retain last state - eliminates need for external latch ICs in hold-mode applications like status register buffering. |
| TTL-Compatible Interface | VIL = 0.8 V, VIH = 2.0 V - interoperable with legacy 74LS, 74ALS, and microcontroller GPIOs without level shifters. |
| Robust Absolute Ratings | 7 V max VCC and VI, –65°C to +150°C storage - withstands transient overvoltage and thermal stress during rework or harsh storage. |
Applications
| Industrial Backplane Interface | Legacy Memory Bus Isolation |
|---|---|
|
Use Scenario: Bidirectional communication between CPU and peripheral modules on a 20-slot industrial backplane using shared address/data lines. IC Role / Device Role / Timing Role: Octal transceiver managing A/B bus direction under handshake control; provides electrical isolation and drive strength for 15 cm trace lengths. Use Value: Open-collector outputs allow multiple modules to share the same bus segment via wired-AND arbitration; 24 mA sink current ensures reliable LOW assertion across all slots. |
Use Scenario: Isolating Z80-based memory expansion cards from main system bus during DMA cycles to prevent contention. IC Role / Device Role / Timing Role: Direction-controlled buffer enabling read/write bursts from RAM banks while blocking upstream traffic during refresh. Use Value: Dual OE inputs permit precise timing alignment with WAIT and MREQ signals; sub-10 ns propagation delay avoids cycle stretching in 4 MHz Z80 systems. |
| Programmable Logic Interconnect | TTL-Level Serial Control Bus |
|
Use Scenario: Glue logic between GAL16V8 CPLD and 74ALS peripheral chips in test equipment control plane. IC Role / Device Role / Timing Role: Signal translator and driver for configurable I/O pins, supporting both input capture and output assertion modes. Use Value: True logic polarity preserves CPLD output states; open-collector outputs interface directly with GAL's 5 V-tolerant I/O without series resistors. |
Use Scenario: Bidirectional serial command bus linking microcontroller UART to multiple sensor nodes using half-duplex RS-485-like topology. IC Role / Device Role / Timing Role: Local bus repeater and level shifter, converting MCU GPIO signals to robust open-collector bus drivers. Use Value: 48 mA sink capability (in -1 variant) drives long cables with heavy capacitive load; bus-latch mode holds last command during node power-up sequencing. |
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; higher ICC (39–50 mA) but lower VOL (0.25 V @ 12 mA). | Requires separate bus contention management; unsuitable for wired-AND or multi-drop pull-up topologies. | Select when clean 3-state isolation is needed and external pull-ups are undesirable. |
| SN74AS623 | Faster propagation (1–9 ns), higher IOL (64 mA), AS-family speed; incompatible with ALS timing margins and power budget. | Not drop-in: increased ICC (16–189 mA) demands heavier decoupling; may overload legacy 5 V supplies. | Choose only for new designs requiring >25 MHz bus rates and verified supply headroom. |
Compared with SN74ALS621ADWR, SN74ALS623ADW offers cleaner 3-state control but forfeits wired-AND capability, while SN74AS623 delivers speed at the cost of power and compatibility - making SN74ALS621ADWR the optimal choice for established TTL bus architectures requiring open-collector flexibility and proven reliability.
Availability
SN74ALS621ADWR is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory bus isolation, programmable logic interconnect, and TTL-level serial control bus applications requiring stable component supply and long-term obsolescence mitigation.
Supply support for SN74ALS621ADWR 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 founded in 1930, specializing in analog, embedded processing, and logic solutions with broad industrial, automotive, and communications reach.
The SN74ALS621ADWR belongs to TI's legacy 74ALS logic family, engineered for high-reliability, 5 V TTL-compatible digital interfacing in industrial control, test equipment, and retro-computing systems where speed, noise immunity, and long-term availability are critical.
FAQ
What is the output configuration of the SN74ALS621ADWR?
The SN74ALS621ADWR features open-collector outputs on both A and B ports. This means each I/O line can only actively drive LOW or float (high-impedance); external pull-up resistors are required to establish a logic HIGH level. This configuration enables wired-AND bus sharing, level translation, and multi-driver arbitration - a key distinction from 3-state alternatives like SN74ALS623ADW. The SN74ALS621ADWR does not provide active HIGH drive capability.
Does the SN74ALS621ADWR support 3.3 V operation?
No, the SN74ALS621ADWR is strictly a 5 V device. Its recommended operating conditions specify VCC = 4.5 V to 5.5 V, and its input thresholds (VIH = 2.0 V, VIL = 0.8 V) and output characteristics are optimized for TTL-level signaling. Applying 3.3 V to VCC will result in undefined logic behavior, insufficient noise margin, and potential failure to meet VOL or VOH specifications. For 3.3 V systems, consider modern level translators or voltage-tolerant logic families instead of the SN74ALS621ADWR.
How does bus-latch functionality work on the SN74ALS621ADWR?
When both OEAB and OEBA are driven LOW, the SN74ALS621ADWR enters bus-latch mode: both A and B ports retain their last driven states, even if all other drivers on the buses go high-impedance. This occurs because each output reinforces its corresponding input in this dual-enabled configuration. The SN74ALS621ADWR thus acts as a passive 16-bit latch without clocks or additional components - ideal for holding status registers or control words during system reset or power sequencing.
What is the difference between SN74ALS621ADWR and SN74ALS621A-1N?
The SN74ALS621ADWR (SOIC-20, DW package) and SN74ALS621A-1N (PDIP-20, N package) share identical logic function, pinout, and electrical specs, but differ in packaging and drive strength. The "-1" suffix in SN74ALS621A-1N indicates enhanced low-level output current: 48 mA vs. 24 mA for the standard version. The SN74ALS621ADWR is the standard (non-"-1") SOIC variant, rated for 24 mA IOL. Always verify the specific part number's datasheet table - the SN74ALS621ADWR does not support 48 mA drive.
Can the SN74ALS621ADWR replace SN74ALS620ADWR in a design?
No - the SN74ALS621ADWR and SN74ALS620ADWR have opposite logic polarity and output types. SN74ALS620ADWR is inverting with 3-state outputs, while SN74ALS621ADWR is non-inverting with open-collector outputs. Swapping them would invert data and eliminate wired-AND capability, causing functional failure. Their function tables and output structures are mutually incompatible; no direct substitution is possible without board-level redesign and logic inversion compensation.
SN74ALS621ADWR 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
SN74ALS621ADWR FAQ
1.How can I place an order for SN74ALS621ADWR through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621ADWR 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 SN74ALS621ADWR reliable?
The price and inventory of SN74ALS621ADWR are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621ADWR is usually 5 days.
3.What payment methods are accepted for SN74ALS621ADWR?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS621ADWR transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS621ADWR?
SN74ALS621ADWR orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS621ADWR 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 SN74ALS621ADWR?
For technical support, including SN74ALS621ADWR datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621ADWR requirements.
6.How does Aetrix verify that SN74ALS621ADWR is sourced from the original manufacturer or authorized distributors?
All SN74ALS621ADWR 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 SN74ALS621ADWR meets industry standards.
7.What is the process for return or replacement of SN74ALS621ADWR?
All SN74ALS621ADWR units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621ADWR, 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 SN74ALS621ADWR part is unused and in its original packaging.
Return procedure for SN74ALS621ADWR:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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