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Texas Instruments SN74LS243N
- Part No.:
- SN74LS243N
- Manufacturer:
- Texas Instruments
- Package:
- 14-DIP (0.300", 7.62mm)
- Datasheet:
-
SN74LS243N.pdf
- Description:
- IC TXRX NON-INVERT 5.25V 14DIP
- Quantity:
- Payment:
- Shipping:
Inventory:362
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Product details
Overview
SN74LS243N from Texas Instruments is a quadruple bus transceiver IC designed for asynchronous two-way communication between data buses. It features PNP inputs to reduce DC loading, 400 mV typical input hysteresis for improved noise margin, and supports bidirectional data flow (A↔B) with isolation and latch modes. It operates from 0°C to 70°C and drives terminated lines down to 133 Ω.
For engineers reviewing the SN74LS243N datasheet, SN74LS243N pinout, SN74LS243N application, or SN74LS243N equivalent, key selection criteria include its 14-pin PDIP package, TTL-compatible logic levels, ±12 mA output drive capability, propagation delays under 18 ns, and dual enable control (GAB/GBA) for direction management in legacy bus systems.
Technical Context
The SN74LS243N implements four independent bidirectional data channels, each controlled by separate active-low GAB (A-to-B enable) and GBA (B-to-A enable) signals. Its PNP-input structure lowers input current draw, while internal hysteresis enhances immunity to slow-rising or noisy bus signals.
Directional control is fully asynchronous: simultaneous assertion of both enables results in latched A = B state, while deassertion isolates both buses. Output drivers meet standard LS-TTL specifications-VOH ≥ 2.4 V at –12 mA, VOL ≤ 0.5 V at 24 mA-with ICC ≤ 54 mA when all transceivers are enabled.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Supply Voltage | 4.75–5.25 V - Ensures stable operation within standard TTL rail tolerance |
| Input Hysteresis | Typ. 400 mV - Increases noise immunity on shared or unterminated data buses |
| Output Drive | –12 mA (high), +24 mA (low) - Sufficient to drive multiple LS loads or 133-Ω terminated lines |
| Propagation Delay | tPLH/tPHL ≤ 18 ns - Supports bus speeds up to ~30 MHz in point-to-point configurations |
| Operating Temp | 0°C to 70°C - Qualified for commercial-grade embedded and industrial control applications |
| Enable Logic | Active-low GAB & GBA - Enables flexible bus arbitration without external inverters |
Pinout & Package
SN74LS243N is housed in a 14-pin plastic dual in-line package (PDIP-N), 0.300-inch width, with standard through-hole mounting and RoHS-compliant NiPdAu lead finish.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1, 13 | GAB, GBA | Active-low enables: GAB = low enables A→B; GBA = low enables B→A |
| 2, 4, 5, 6 | A1–A4 | Bus A side inputs/outputs - Connects to source data bus |
| 3, 11, 10, 9 | B1–B4 | Bus B side inputs/outputs - Connects to destination data bus |
| 7 | GND | Ground reference for logic and power return path |
| 14 | VCC | +5 V supply - Powers internal TTL circuitry and output drivers |
| 8 | NC | No connect - Internally unconnected; must remain floating or grounded per layout best practice |
Key Features
| Feature | Design Value |
|---|---|
| Quadruple bidirectional channels | Four independent A↔B data paths in one IC - reduces board space vs. discrete buffers |
| PNP input structure | Reduces input current to ≤ –0.2 mA - minimizes loading on upstream TTL or CMOS drivers |
| Dual active-low direction control | GAB and GBA allow asymmetric bus arbitration - e.g., A→B only while B remains isolated |
| Hysteresis-enhanced inputs | 400 mV threshold separation - prevents chatter on slow or noisy bus transitions |
| Latch mode (GAB = H, GBA = H) | Freezes A = B state - useful for hold/transparent latch functions without external storage |
Applications
| Industrial PLC Backplane Interface | Legacy Computer Memory Expansion Bus |
|---|---|
Use Scenario: Interfacing microcontroller-based I/O modules to a shared 8-bit parallel backplane in programmable logic controllers. IC Role / Device Role / Timing Role: Bidirectional bus transceiver managing data flow between CPU and peripheral cards under address-decoded GAB/GBA control. Use Value: Enables hot-swap-capable module insertion via isolation mode (GAB = GBA = H), preventing bus contention during card replacement. | Use Scenario: Extending memory address/data bus between mainboard and add-in RAM cards in 1980s-era desktop computers. IC Role / Device Role / Timing Role: Level-shifting and direction-controlled data coupling between CPU and memory banks operating at different timing phases. Use Value: Supports 133-Ω terminated bus stubs with sub-18 ns delays - maintains signal integrity across multi-card expansion architectures. |
| Test Equipment Digital Pattern Generator | Automated Test Fixture Data Mux |
Use Scenario: Routing stimulus patterns from pattern generator ASIC to DUT pins while capturing response data on same lines. IC Role / Device Role / Timing Role: Reconfigurable bidirectional data path synchronized to test clock edges using GAB/GBA strobes. Use Value: Eliminates need for separate driver/receiver pairs - cuts component count and routing complexity in compact ATE PCBs. | Use Scenario: Multiplexing shared digital I/O lines among multiple sensor interfaces in production line functional testers. IC Role / Device Role / Timing Role: Direction-controlled bus switch enabling one master controller to read from or write to any selected sensor channel. Use Value: Latch mode (GAB = GBA = H) holds last transmitted value during sensor settling time - improves measurement repeatability. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar bus transceiver applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74LS245N | Octal (8-bit), single-directional with DIR pin - no native A↔B bidirectionality | Requires external logic to emulate bidirectional flow; higher pin count | Choose when higher channel density is needed and direction control can be centralized |
| SN74ALS243N | Advanced LS variant: lower ICC (25 mA max), faster tPLH/tPHL (11 ns typ), same pinout | Direct drop-in replacement with improved speed/power - requires validation of ALS input thresholds | Prefer for new designs where reduced power and tighter timing margins are critical |
Compared with SN74LS245N, SN74LS243N provides true bidirectional per-channel control without external logic; compared with SN74ALS243N, it offers broader voltage tolerance (4.75–5.25 V vs. 4.5–5.5 V) and higher noise immunity due to larger hysteresis, making it more robust in electrically noisy industrial environments.
Availability
SN74LS243N is available at Aetrix Electronics and suitable for industrial PLC backplanes, legacy computer bus extensions, automated test fixture I/O multiplexing, and digital pattern generator interfaces requiring stable component supply over extended production lifecycles.
Supply support for SN74LS243N 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 SN74LS243N belongs to TI's legacy 74LS logic family, engineered specifically for reliable, low-cost bidirectional bus interfacing in commercial-temperature embedded systems and retro-computing hardware.
FAQ
What is the maximum bus termination impedance supported by SN74LS243N?
The SN74LS243N is specified to drive terminated lines down to 133 Ω, as confirmed in the device description section of the TI datasheet SDLS145A. This capability stems from its ±12 mA/±24 mA output drive strength and TTL-compatible output structure. For heavier loads or longer traces, verify signal integrity with oscilloscope measurements at the far end of the bus, especially under worst-case temperature and voltage conditions.
Does SN74LS243N support hot-swapping of bus-connected modules?
Yes - SN74LS243N supports hot-swap operation via its isolation mode: asserting both GAB and GBA high (logic 1) places all A and B terminals in high-impedance state, disconnecting both buses electrically. This prevents signal contention during module insertion/removal. However, system-level protection (e.g., series resistors, TVS diodes) is still recommended to suppress transient coupling during physical connection.
Can SN74LS243N be used with 3.3 V logic systems?
No - SN74LS243N is a 5 V-only TTL device. Its input thresholds (VIH = 2.0 V min, VIL = 0.8 V max) and output levels (VOH ≈ 2.4–2.7 V, VOL ≈ 0.25–0.5 V) are incompatible with 3.3 V CMOS logic without level translation. Direct connection risks marginal switching, excessive input current, or damage if 3.3 V outputs drive SN74LS243N inputs beyond its –0.5 V absolute minimum VI rating.
What is the function of the NC pin on SN74LS243N?
Pin 8 of SN74LS243N is marked NC (No Connect) in the official TI datasheet SDLS145A and has no internal connection. It must remain unconnected - neither tied to VCC nor GND - to avoid unintended parasitic coupling or mechanical stress on the bond wire. PCB layout should omit copper pad or trace at this location, or use a non-plated through-hole if mechanical stability is required.
How does the latch mode (GAB = H, GBA = H) operate in SN74LS243N?
In latch mode, SN74LS243N forces A1–A4 = B1–B4 transparently, holding the instantaneous data values present at the moment both enables go high. This is not a storage register - it relies on bus capacitance and driver strength to maintain state. Use is limited to short-duration hold applications (e.g., during ADC conversion); for reliable storage, pair SN74LS243N with external latches like SN74LS373.
SN74LS243N Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- 74LS
- Package/Case:
- 14-DIP (0.300", 7.62mm)
- Packaging:
- Bulk
- Product Status:
- Active
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 4
- Input Type:
- -
- Output Type:
- Push-Pull
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.75V ~ 5.25V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 14-PDIP
SN74LS243N FAQ
1.How can I place an order for SN74LS243N through Aetrix?
Please submit a Request for Quotation (RFQ) for SN74LS243N 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 SN74LS243N reliable?
The price and inventory of SN74LS243N are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for SN74LS243N is usually 5 days.
3.What payment methods are accepted for SN74LS243N?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for SN74LS243N transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for SN74LS243N?
SN74LS243N orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your SN74LS243N 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 SN74LS243N?
For technical support, including SN74LS243N datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your SN74LS243N requirements.
6.How does Aetrix verify that SN74LS243N is sourced from the original manufacturer or authorized distributors?
All SN74LS243N 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 SN74LS243N meets industry standards.
7.What is the process for return or replacement of SN74LS243N?
All SN74LS243N units undergo pre-shipment inspection (PSI). If there is an issue with SN74LS243N, 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 SN74LS243N part is unused and in its original packaging.
Return procedure for SN74LS243N:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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