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Texas Instruments SN74ALS621ANG4
- Part No.:
- SN74ALS621ANG4
- Manufacturer:
- Texas Instruments
- Package:
- 20-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74ALS621ANG4.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 20DIP
- Quantity:
- Payment:
- Shipping:
Inventory:2,710
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Product details
Overview
SN74ALS621ANG4 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 features dual output-enable controls (OEAB/OEBA), local bus-latch capability via simultaneous enable, and operates across 0°C to 70°C at 4.5–5.5 V supply. Used in legacy industrial backplanes and memory-mapped I/O interfaces.
For engineers reviewing the SN74ALS621ANG4 datasheet, SN74ALS621ANG4 pinout, SN74ALS621ANG4 application, or SN74ALS621ANG4 equivalent, key selection criteria include its open-collector drive strength (IOL = 24 mA standard / 48 mA in -1 version), bus-isolation behavior under dual-OE control, latch-mode operation, and compatibility with 300-mil PDIP packaging.
Technical Context
This device implements a dual-bus transceiver architecture with independent A→B and B→A data paths controlled by OEAB and OEBA. Its open-collector outputs require external pull-up resistors and support wired-AND logic, enabling shared-bus arbitration in multi-master systems.
The simultaneous assertion of OEAB and OEBA places all outputs in high-impedance while reinforcing input states - allowing 16-bit bus state retention without external latches. Unlike SN74ALS620A (inverting) or SN74ALS623A (3-state), SN74ALS621A provides true-level transmission with open-collector flexibility.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Logic Type | True (non-inverting) data path - preserves signal polarity during A↔B transfer. |
| Output Type | Open-collector - enables wired-AND bus sharing and level translation with external pull-ups. |
| IOL (Standard) | 24 mA sink current - supports driving multiple TTL loads or higher-capacitance buses. |
| IOL (-1 version) | 48 mA sink current - validated only at VCC = 4.75–5.25 V; used in high-drive legacy backplanes. |
| Propagation Delay | 5–20 ns (A↔B), 10–39 ns (OE→output) - meets timing budgets for 20–30 MHz synchronous bus cycles. |
| Supply Voltage | 4.5–5.5 V - compatible with standard +5 V TTL power rails and regulated 5 V supplies. |
| Operating Temp | 0°C to 70°C - qualified for commercial/industrial ambient environments, not extended temp. |
Pinout & Package
SN74ALS621ANG4 is supplied in a 20-pin plastic DIP (N package), 300-mil width, with standard through-hole footprint and JEDEC MS-001 compliant dimensions. Pin 1 is located at the left end of the top row, identified by a beveled corner or notch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (OEAB) | A-to-B Output Enable | Active-low control: enables A→B data flow when low; disables (high-Z) when high. |
| 2–9 (A1–A8) | Bus A Data Inputs/Outputs | Open-collector I/O pins - driven by A-side logic; require external pull-up for logic high. |
| 10 (GND) | Ground Reference | Primary return path for all internal logic and output currents. |
| 11–18 (B1–B8) | Bus B Data Inputs/Outputs | Open-collector I/O pins - driven by B-side logic; require external pull-up for logic high. |
| 19 (OEBA) | B-to-A Output Enable | Active-low control: enables B→A data flow when low; disables (high-Z) when high. |
| 20 (VCC) | Power Supply | +5 V nominal supply input; decoupling capacitor required near pin for noise immunity. |
Key Features
| Feature | Design Value |
|---|---|
| Dual-output-enable control | Enables independent A→B or B→A directionality, or simultaneous isolation of both buses. |
| Local bus-latch mode | Asserting both OEAB and OEBA retains last valid logic states on A and B buses without external latches. |
| True logic polarity | Preserves signal integrity across bidirectional paths - critical for address/data bus mirroring. |
| Open-collector outputs | Supports wired-AND arbitration, mixed-voltage interfacing, and fail-safe bus termination. |
| TTL-compatible interface | Meets ALS family VIH/VIL thresholds (2.0 V / 0.8 V) and drives standard TTL fan-out (10). |
Applications
| Industrial Backplane Interface | Legacy Memory-Mapped I/O |
|---|---|
Use Scenario: Interfacing microprocessor address/data buses to modular I/O cards in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing A/B bus handshaking with cycle-synchronized OE control. Use Value: Enables hot-swappable card insertion via bus isolation and eliminates need for discrete bus buffers or latches. |
Use Scenario: Connecting Z80 or 8085 CPU buses to peripheral ASICs requiring separate read/write strobes and direction control. IC Role / Device Role / Timing Role: True-polarity transceiver supporting memory-mapped register access with OEAB/OEBA timed to RD/WR cycles. Use Value: Maintains signal polarity across bus segments, simplifying timing analysis and reducing PCB trace inversion layers. |
| Multi-Master Bus Arbitration | Level-Shifted Control Bus |
Use Scenario: Shared control bus among multiple microcontrollers in distributed automation nodes. IC Role / Device Role / Timing Role: Open-collector transceiver implementing wired-AND arbitration with pull-up resistor network. Use Value: Allows any node to assert bus control without contention; OE signals coordinate master handoff. |
Use Scenario: Translating 5 V TTL control signals to 3.3 V or 2.5 V logic domains using external pull-up to lower voltage rail. IC Role / Device Role / Timing Role: Level-shifting transceiver leveraging open-collector outputs and dual-supply pull-ups. Use Value: Eliminates need for dedicated level translators; supports mixed-voltage system integration with minimal components. |
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 timing. | Requires bus-hold or termination for floating states; unsuitable for wired-AND. | Select when bus isolation without external pull-ups is preferred and no wired-AND is needed. |
| SN74ALS620AN | Inverting logic; 3-state outputs; identical package and pinout. | Introduces signal inversion - requires logic compensation in data path. | Select only if system design accommodates inverted data or uses complementary signaling. |
Compared with SN74ALS621ANG4, SN74ALS623AN offers simpler termination but lacks wired-AND capability, while SN74ALS620AN introduces functional asymmetry via inversion - making SN74ALS621ANG4 uniquely suited for polarity-critical, multi-master bus designs.
Availability
SN74ALS621ANG4 is available at Aetrix Electronics and suitable for industrial backplane interfaces, legacy memory-mapped I/O subsystems, and multi-master control bus implementations requiring stable component supply and long-term obsolescence management.
Supply support for SN74ALS621ANG4 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 for industrial, automotive, and communications markets.
SN74ALS621ANG4 belongs to the ALS (Advanced Low-Power Schottky) logic family, engineered for high-speed, low-power TTL-compatible operation in mission-critical industrial control and computing infrastructure.
FAQ
What is the function of OEAB and OEBA on the SN74ALS621ANG4?
OEAB (pin 1) enables data flow from bus A to bus B when low; OEBA (pin 19) enables data flow from bus B to bus A when low. Both can be asserted simultaneously to place all outputs in high-impedance while retaining bus states - a feature known as local bus-latch mode. This behavior is intrinsic to the SN74ALS621ANG4's internal architecture and does not require external clocking or latching circuitry.
Does SN74ALS621ANG4 support 3.3 V logic levels?
No - SN74ALS621ANG4 is a 5 V-only TTL device with VIH = 2.0 V and VIL = 0.8 V, designed for 5 V operation (4.5–5.5 V). Its open-collector outputs can interface to 3.3 V buses using an external pull-up to 3.3 V, but input thresholds and internal logic remain 5 V referenced. Direct connection to 3.3 V CMOS inputs without level shifting may cause unreliable switching in the SN74ALS621ANG4.
Is SN74ALS621ANG4 pin-compatible with SN74ALS623AN?
Yes - SN74ALS621ANG4 and SN74ALS623AN share identical 20-pin PDIP (N) packaging, pin numbering, and pin functions. However, SN74ALS621ANG4 has open-collector outputs while SN74ALS623AN uses 3-state totem-pole outputs, so direct substitution requires verifying bus termination and drive requirements in the target application.
What is the maximum sink current rating for SN74ALS621ANG4?
The standard SN74ALS621ANG4 is rated for 24 mA per output (IOL) under recommended conditions. A variant designated SN74ALS621A-1N supports 48 mA IOL, but only when VCC is tightly regulated between 4.75 V and 5.25 V. The SN74ALS621ANG4 itself is the standard version and does not carry the "-1" suffix, so its guaranteed IOL remains 24 mA.
Can SN74ALS621ANG4 be used in new designs today?
Yes - SN74ALS621ANG4 remains actively manufactured and stocked by Texas Instruments and authorized distributors. It is suitable for sustaining legacy equipment, industrial retrofits, and applications where proven reliability, long-term availability, and exact form-fit-function replacement are required. Aetrix Electronics maintains inventory and lifecycle support for SN74ALS621ANG4 in both tube and tape-and-reel formats.
SN74ALS621ANG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74ALS
- Package/Case:
- 20-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Discontinued at Digi-Key
- 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
SN74ALS621ANG4 FAQ
1.How can I place an order for SN74ALS621ANG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS621ANG4 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 SN74ALS621ANG4 reliable?
The price and inventory of SN74ALS621ANG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS621ANG4 is usually 5 days.
3.What payment methods are accepted for SN74ALS621ANG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74ALS621ANG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74ALS621ANG4?
SN74ALS621ANG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS621ANG4 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 SN74ALS621ANG4?
For technical support, including SN74ALS621ANG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS621ANG4 requirements.
6.How does Aetrix verify that SN74ALS621ANG4 is sourced from the original manufacturer or authorized distributors?
All SN74ALS621ANG4 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 SN74ALS621ANG4 meets industry standards.
7.What is the process for return or replacement of SN74ALS621ANG4?
All SN74ALS621ANG4 units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS621ANG4, 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 SN74ALS621ANG4 part is unused and in its original packaging.
Return procedure for SN74ALS621ANG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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