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Texas Instruments SN74ALS621AN
- Part No.:
- SN74ALS621AN
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS621AN.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:1,886
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Product details
Overview
SN74ALS621AN from Texas Instruments is an octal bus transceiver with open-collector outputs and true (non-inverting) logic, designed for asynchronous two-way data communication between A and B buses in TTL-level 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 variant), and features dual output-enable inputs (OEAB/OEBA) enabling bidirectional data flow or bus-latch functionality.
For engineers reviewing the SN74ALS621AN datasheet, SN74ALS621AN pinout, SN74ALS621AN application, or SN74ALS621AN equivalent, this device is selected for legacy industrial control backplanes, parallel I/O expansion interfaces, and TTL-compatible bus isolation where open-collector drive and bus-hold capability are required.
Technical Context
The SN74ALS621AN implements a dual-bus transceiver architecture with independent OEAB (A-to-B enable) and OEBA (B-to-A enable) controls, allowing flexible direction selection and simultaneous enablement for local bus-latching. Its open-collector outputs require external pull-up resistors and support wired-AND logic and level translation when interfaced with higher-voltage buses.
Unlike the inverting SN74ALS620A or 3-state SN74ALS623A/AS623 variants, the SN74ALS621AN provides true logic polarity and relies on external termination for high-level signaling - making it suitable for shared-bus arbitration and interrupt-line aggregation in multi-master systems.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Type | True (non-inverting) - preserves signal polarity across A↔B bus transfer |
| Output Type | Open-collector - enables wired-AND, level shifting, and multi-drop bus sharing |
| VCC Range | 4.5 V to 5.5 V - compatible with standard 5 V TTL power rails |
| IOL (Standard) | 24 mA - drives standard TTL loads with ≤0.5 V VOL at full sink current |
| IOL (-1 Variant) | 48 mA - supports heavier fanout or longer traces without voltage degradation |
| Propagation Delay | 5–33 ns (A↔B) - ensures timing compatibility with 20–30 MHz synchronous bus cycles |
| Operating Temp | 0°C to 70°C - rated for commercial-grade industrial equipment environments |
Pinout & Package
SN74ALS621AN uses a 20-pin plastic DIP (N package), 300-mil width, with 2.54 mm lead pitch and through-hole mounting. Pin 1 is marked by a notch or beveled corner at the top-left of the package body.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OEAB) | A-to-B Output Enable | Active-low control: enables A→B data transmission when low; disables outputs to high-Z |
| 2–9 (A1–A8) | Bus A Data Inputs/Outputs | Open-collector I/O pins connected to A-side bus; driven low or float high via pull-up |
| 10 (GND) | Ground Reference | Power return path for all internal logic and output stages |
| 11 (VCC) | Supply Voltage | +5 V DC supply input for ALS logic core and output drivers |
| 12–19 (B1–B8) | Bus B Data Inputs/Outputs | Open-collector I/O pins connected to B-side bus; identical electrical behavior to A pins |
| 20 (OEBA) | B-to-A Output Enable | Active-low control: enables B→A data transmission when low; isolates B bus otherwise |
Key Features
| Feature | Design Value |
|---|---|
| Open-collector outputs | Enables wired-AND bus arbitration and interface to mixed-voltage systems using external pull-ups |
| Dual independent enables | OEAB and OEBA allow asymmetric bus control - e.g., A→B only while B bus remains isolated |
| Bus-latch capability | Simultaneous OEAB and OEBA assertion holds last valid state on both buses without external latches |
| TTL-compatible thresholds | VIH = 2 V, VIL = 0.8 V - ensures reliable interfacing with legacy 74LS/74ALS logic families |
| ALS process technology | Lower power than standard TTL (ICC ≈ 29–48 mA) with improved noise immunity and speed |
Applications
| Industrial Backplane Interface | Parallel I/O Expansion |
|---|---|
Use Scenario: Connecting microcontroller GPIO ports to a modular rack-mounted I/O chassis with shared address/data lines. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU bus and peripheral slot bus under software-controlled OEAB/OEBA timing. Use Value: Open-collector outputs prevent contention during hot-swap insertion and allow multiple modules to share interrupt lines via wired-AND. |
Use Scenario: Expanding 8-bit parallel port capability on an embedded controller board using off-board peripherals. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled buffer between MCU's native 5 V TTL bus and external 5 V peripheral bus. Use Value: True logic polarity preserves register mapping integrity; dual enables simplify handshaking protocol implementation. |
| Legacy System Bus Isolation | Multi-Master Interrupt Aggregation |
Use Scenario: Isolating two legacy 8-bit data buses in a test instrumentation system to prevent signal corruption during concurrent access. IC Role / Device Role / Timing Role: Controlled isolation gate activated only during synchronized data transfers, minimizing bus loading during idle periods. Use Value: High-impedance disable state eliminates capacitive loading and crosstalk between otherwise coupled buses. |
Use Scenario: Combining interrupt requests from eight discrete sensors onto a single MCU interrupt line. IC Role / Device Role / Timing Role: Wired-AND aggregator using open-collector B-side outputs tied to common interrupt rail with pull-up resistor. Use Value: Eliminates need for external diode-OR network; inherent active-low interrupt polarity matches most MCU inputs. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS623AN | 3-state (not open-collector) outputs; true logic; same pinout and voltage specs | Requires no external pull-ups; unsuitable for wired-AND or level translation | Select when bus isolation without external components is preferred and multi-drop sharing is not needed |
| SN74ALS620AN | Inverting logic; 3-state outputs; identical package and timing | Introduces signal inversion requiring software/hardware compensation in data paths | Select only if inverting behavior aligns with existing bus protocol or simplifies control logic |
Compared with SN74ALS621AN, SN74ALS623AN offers simpler termination but loses wired-AND capability, while SN74ALS620AN adds inversion overhead without functional advantage in true-logic systems - making SN74ALS621AN the optimal choice for open-collector bus arbitration and legacy TTL interconnect.
Availability
SN74ALS621AN is available at Aetrix Electronics and suitable for industrial backplane interfaces, parallel I/O expansion modules, and legacy system bus isolation requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS621AN 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 and automotive reach.
The SN74ALS621AN belongs to TI's legacy 74ALS logic family, engineered for high-speed, low-power TTL-compatible operation in industrial control, test equipment, and computer peripheral interfaces.
FAQ
What is the output configuration of the SN74ALS621AN?
The SN74ALS621AN features open-collector outputs on both A and B ports. This means each output can actively drive low or float high - requiring external pull-up resistors to establish a defined logic-high level. This configuration supports wired-AND logic, bus sharing, and level translation, distinguishing it from 3-state alternatives like SN74ALS623AN. The SN74ALS621AN does not provide active high-drive capability.
Does the SN74ALS621AN support bus-latching functionality?
Yes, the SN74ALS621AN supports bus-latching: when both OEAB and OEBA are asserted low simultaneously, the transceiver enters a mode where each output reinforces its corresponding input. With all other drivers on both A and B buses in high-impedance states, the 16 bus lines retain their last valid logic states - effectively storing data without external latches. This behavior is confirmed in the device function table and description section of the SDAS226A datasheet.
What is the maximum sink current rating for the SN74ALS621AN?
The standard SN74ALS621AN 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). A variant - SN74ALS621A-1N - increases this to 48 mA, but only when VCC is tightly regulated between 4.75 V and 5.25 V. The SN74ALS621AN itself does not carry the "-1" suffix and therefore adheres to the 24 mA specification.
Can the SN74ALS621AN be used as a direct replacement for SN74ALS623AN?
No - the SN74ALS621AN is not a direct replacement for SN74ALS623AN due to fundamental output architecture differences: SN74ALS621AN uses open-collector outputs requiring pull-ups, while SN74ALS623AN uses 3-state totem-pole outputs that actively drive both logic levels. Swapping them requires circuit redesign, including removal of pull-ups and verification of bus contention behavior. Pinout and voltage specs match, but functional substitution is not drop-in.
What package type is used for the SN74ALS621AN?
The SN74ALS621AN uses a 20-pin plastic dual in-line package (PDIP-N), 300-mil width, with through-hole leads spaced at 2.54 mm. It is distinct from the SOIC (DW) variant SN74ALS621ADW. The N package is RoHS-compliant, has no moisture sensitivity level (MSL) rating, and is intended for wave soldering or manual assembly in prototyping and low-volume industrial applications.
SN74ALS621AN Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- 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:
- Through Hole
- Supplier Device Package:
- 20-PDIP
SN74ALS621AN FAQ
1.How can I place an order for SN74ALS621AN through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621AN 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 SN74ALS621AN reliable?
The price and inventory of SN74ALS621AN are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621AN is usually 5 days.
3.What payment methods are accepted for SN74ALS621AN?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS621AN transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS621AN?
SN74ALS621AN orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS621AN 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 SN74ALS621AN?
For technical support, including SN74ALS621AN datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621AN requirements.
6.How does Aetrix verify that SN74ALS621AN is sourced from the original manufacturer or authorized distributors?
All SN74ALS621AN 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 SN74ALS621AN meets industry standards.
7.What is the process for return or replacement of SN74ALS621AN?
All SN74ALS621AN units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621AN, 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 SN74ALS621AN part is unused and in its original packaging.
Return procedure for SN74ALS621AN:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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