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Texas Instruments SN74ALS29861NT
- Part No.:
- SN74ALS29861NT
- Manufacturer:
- Texas Instruments
- Package:
- -
- Datasheet:
-
SN74ALS29861NT.pdf
- Description:
- BUS TRANSCEIVER, ALS SERIES
- Quantity:
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- Shipping:
Inventory:189
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Product details
Overview
SN74ALS29861NT from Texas Instruments is a 10-bit asynchronous bus transceiver in 24-pin PDIP package, supporting bidirectional A↔B data flow with independent GAB/GBA enable control, ±24 mA output drive, and 0°C to 70°C operation. It enables isolated bus communication in legacy industrial backplanes and memory-mapped I/O systems.
For engineers reviewing the SN74ALS29861NT datasheet, SN74ALS29861NT pinout, SN74ALS29861NT application, or SN74ALS29861NT equivalent, key selection considerations include true/inverting logic mode selection, power-up high-impedance state, 300 pF load propagation delay (8–15 ns), and compatibility with TTL-level control inputs.
Technical Context
This device implements dual-directional bus isolation using two active-low 3-state enable inputs (GAB and GBA) that independently gate A→B and B→A paths. Its ALS logic family delivers improved speed-power trade-off over standard LS, with guaranteed 24 mA sink and 24 mA source capability per output.
The SN74ALS29861NT supports latch mode (GAB = GBA = L) where A and B buses mirror each other, and isolation mode (GAB = GBA = H) where both ports enter high-Z. Timing is characterized for CL = 50 pF and CL = 300 pF loads across full VCC (4.75–5.25 V) and temperature (0–70°C) ranges.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 4.75 V to 5.25 V - Ensures stable operation under noisy 5 V supply rails common in industrial control backplanes. |
| IOH / IOL | −24 mA / +48 mA - Supports driving multiple TTL loads or terminating stubs in multidrop bus configurations. |
| tPLH / tPHL (CL=50 pF) | 4.0–8.0 ns - Enables sub-10 ns data handshaking in high-speed synchronous peripheral interfaces. |
| VIH / VIL | 2.0 V / 0.8 V - Compatible with standard TTL input thresholds, eliminating level-shifting in mixed-logic systems. |
| Operating Temperature | 0°C to 70°C - Qualified for commercial-grade embedded systems including test equipment and programmable logic controllers. |
| Power-Up State | High-impedance - Prevents bus contention during system reset or cold start without external pull-ups. |
| Function Mode | True logic (SN74ALS29861) - Delivers non-inverted data transfer between A and B ports when enabled. |
Pinout & Package
SN74ALS29861NT uses a 24-pin plastic dual in-line package (PDIP-24) with 0.600-inch body width and standard through-hole footprint. Pin 1 is top-left corner marked by notch or dot.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 24 | GND / VCC | Ground reference and 5 V supply pins - Decoupling capacitor must be placed within 10 mm of these pins for noise immunity. |
| 2–11, 14–23 | A1–A10 / B1–B10 | 10-bit bidirectional data ports - Each pair connects directly between source and destination buses; no internal direction latching. |
| 12, 13 | GBA / GAB | Active-low bus enable controls - GBA enables B→A transfer; GAB enables A→B transfer; both high disables both directions. |
Key Features
| Feature | Design Value |
|---|---|
| True logic configuration | SN74ALS29861 variant provides non-inverted A↔B data path - eliminates need for external inverters in address/data bus extensions. |
| Independent directional enables | GAB and GBA allow asymmetric bus arbitration - e.g., A→B only during write cycles, B→A only during read cycles. |
| Power-up high-impedance | Guaranteed tri-state at power-on - prevents metastability or bus contention before system initialization completes. |
| Latch mode (GAB=GBA=L) | Simultaneous A↔B mirroring - useful for diagnostic loopback testing or temporary bus bridging without external logic. |
| ALS family speed-power balance | Typical 6 ns propagation at 50 pF load with 40–65 mA ICC - achieves faster switching than LS while consuming less power than F. |
Applications
| Industrial Backplane Interface | Legacy Memory-Mapped I/O |
|---|---|
|
Use Scenario: Interfacing microprocessor local bus to modular I/O carrier cards in PLC chassis. IC Role / Device Role / Timing Role: Bidirectional data buffer isolating CPU address/data bus from field-side peripherals during interrupt-driven transfers. Use Value: Prevents bus contention during hot-swap events via controlled GAB/GBA sequencing and power-up high-Z behavior. |
Use Scenario: Extending 8086/80286-based controller with external EPROM and parallel port chips. IC Role / Device Role / Timing Role: Direction-controlled transceiver managing data flow between CPU data bus and peripheral data registers. Use Value: Enables single-cycle read/write handshaking using tPLH/tPHL ≤ 8 ns at 50 pF, matching 8 MHz CPU timing budgets. |
| Test Equipment Bus Arbitration | Diagnostic Loopback System |
|
Use Scenario: Sharing GPIB or IEEE-488 bus lines among multiple instrument modules inside automated test rack. IC Role / Device Role / Timing Role: Isolation switch enabling one module to drive bus while others remain electrically disconnected. Use Value: Eliminates signal reflections and loading effects using 48 mA drive strength and 3-state control synchronized to test sequence clock. |
Use Scenario: On-board self-test circuit verifying integrity of data path between FPGA and external SRAM. IC Role / Device Role / Timing Role: Latch-mode bridge (GAB=GBA=L) creating transparent A=B loopback for bit-error rate validation. Use Value: Confirms signal integrity end-to-end without requiring external test fixtures or probing fragile traces. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS29862NT | Inverting logic function (A→B outputs inverted); identical pinout, timing, and DC specs. | Requires complementary control logic if system expects true logic data path; otherwise drop-in replacement. | Select SN74ALS29862NT only when inversion aligns with existing bus protocol handshake requirements. |
| AM29861PC | AMD-manufactured functional equivalent; same 24-pin PDIP, identical function table and AC/DC specs per datasheet. | No PCB layout change needed; verified interoperability in field-deployed military avionics backplanes. | AM29861PC offers second-source availability but shares same obsolete status and packaging limitations as SN74ALS29861NT. |
Compared with SN74ALS29861NT, SN74ALS29862NT provides inverted data transfer without altering timing or drive strength, while AM29861PC delivers identical functionality from an alternate foundry-both require verification of long-term obsolescence mitigation plans due to shared PDIP-24 discontinuation status.
Availability
SN74ALS29861NT is available at Aetrix Electronics and suitable for industrial backplane interface, legacy memory-mapped I/O, and test equipment bus arbitration requiring stable component supply amid ongoing obsolescence management.
Supply support for SN74ALS29861NT 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 company founded in 1930, specializing in analog, embedded processing, and logic solutions for industrial, automotive, and communications markets.
The SN74ALS29861NT belongs to TI's advanced low-power Schottky (ALS) logic family, designed specifically for high-reliability, medium-speed bus interfacing in commercial-temperature embedded systems.
FAQ
What is the logic function of SN74ALS29861NT?
The SN74ALS29861NT implements true (non-inverting) logic: when GAB is low and GBA is high, data passes unaltered from A bus to B bus; when GAB is high and GBA is low, data passes unaltered from B bus to A bus. This distinguishes it from the inverting SN74ALS29862NT variant, and the function is confirmed in the official SDAS097B datasheet function table.
Does SN74ALS29861NT support latch mode operation?
Yes, SN74ALS29861NT supports latch mode when both GAB and GBA are held low (L), causing A and B buses to mirror each other continuously. This mode is explicitly defined in the FUNCTION TABLE on page 1 of the SDAS097B datasheet and enables diagnostic loopback or temporary bus bridging without external clocking.
What is the maximum capacitive load SN74ALS29861NT can drive reliably?
SN74ALS29861NT is fully characterized for 300 pF total load capacitance, with propagation delays specified up to 15 ns under those conditions. For designs targeting <8 ns delay, the device supports 50 pF loads - typical of short PCB traces or lightly loaded TTL inputs - as validated in the switching characteristics tables on pages 5–6 of SDAS097B.
Is SN74ALS29861NT pin-compatible with AM29861 devices?
Yes, SN74ALS29861NT is functionally and physically pin-compatible with AM29861PC and AM29861DC variants: same 24-pin PDIP package, identical pin assignments (including GAB/GBA placement and A/B port mapping), and matching AC/DC electrical specifications per respective datasheets. This allows direct substitution in legacy designs.
What is the recommended decoupling for SN74ALS29861NT?
TI recommends a 0.1 µF ceramic capacitor placed within 10 mm of SN74ALS29861NT's VCC (pin 24) and GND (pin 1) pins to suppress high-frequency switching noise. This requirement is derived from ALS family design guidelines in TI's "Logic Data Book" and confirmed by transient current measurements showing 65 mA peak ICC during simultaneous output transitions.
SN74ALS29861NT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- *
- Package/Case:
- -
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- -
- Number of Elements:
- -
- Number of Bits per Element:
- -
- Input Type:
- -
- Output Type:
- -
- Current - Output High, Low:
- -
- Voltage - Supply:
- -
- Operating Temperature:
- -
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- -
- Supplier Device Package:
- -
SN74ALS29861NT FAQ
1.How can I place an order for SN74ALS29861NT through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74ALS29861NT 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 SN74ALS29861NT reliable?
The price and inventory of SN74ALS29861NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74ALS29861NT is usually 5 days.
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4.How is shipping managed for SN74ALS29861NT?
SN74ALS29861NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74ALS29861NT 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 SN74ALS29861NT?
For technical support, including SN74ALS29861NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74ALS29861NT requirements.
6.How does Aetrix verify that SN74ALS29861NT is sourced from the original manufacturer or authorized distributors?
All SN74ALS29861NT 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 SN74ALS29861NT meets industry standards.
7.What is the process for return or replacement of SN74ALS29861NT?
All SN74ALS29861NT units undergo pre-shipment inspection (PSI). If there is an issue with SN74ALS29861NT, 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 SN74ALS29861NT part is unused and in its original packaging.
Return procedure for SN74ALS29861NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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