My Inquiry
My Account
onsemi DM74ALS646NT
- Part No.:
- DM74ALS646NT
- Manufacturer:
- onsemi
- Package:
- 24-DIP (0.300", 7.62mm)
- Datasheet:
-
DM74ALS646NT.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,133
Please send an inquiry. Send us your inquiry, and we will respond immediately.
Product details
Overview
DM74ALS646NT from Fairchild Semiconductor is an octal 3-STATE bus transceiver and register with independent A/B registers, dual clock inputs (CAB/CBA), dual select controls (SAB/SBA), and direction/enable logic (DIR/G). It operates at 5V, supports 40 MHz clock frequency, delivers ±24 mA output drive, and is packaged in a 24-pin PDIP for legacy board-level integration in industrial control backplanes.
For engineers reviewing the DM74ALS646NT datasheet, pinout, applications, or equivalent options, key selection criteria include real-time vs. registered data multiplexing capability, make-before-break select logic, 3-STATE bus driving without pull-ups, and compatibility with TTL-level system buses requiring bidirectional buffered data flow between CPU and peripheral subsystems.
Technical Context
The DM74ALS646NT implements two independent edge-triggered D-type flip-flop registers-one for bus A (clocked by CAB) and one for bus B (clocked by CBA)-enabling synchronous storage of 8-bit data on positive clock transitions. Its 3-STATE totem-pole outputs support direct bus connection with no external termination.
Four functional modes are controlled via G (enable) and DIR (direction): real-time A→B or B→A transfer, simultaneous A/B register loading, or isolated stored-data output to either bus. SAB/SBA provide glitch-free switching between real-time and registered data paths using make-before-break logic.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC | 5 V nominal supply - compatible with standard TTL logic rails and legacy 5V system power domains |
| fCLK | 40 MHz max clock frequency - supports high-speed register capture in microprocessor address/data latching |
| IOL / IOH | 24 mA sink / −15 mA source - drives heavy capacitive buses directly without buffer amplification |
| tPLH / tPHL | 5–30 ns propagation delay - ensures timing compliance in 20–25 ns cycle time bus systems |
| VIH / VIL | 2.0 V min HIGH / 0.8 V max LOW - guarantees robust noise margin against TTL-compatible signal sources |
| TA Operating Range | 0°C to +70°C - rated for commercial-grade industrial control and instrumentation environments |
Pinout & Package
DM74ALS646NT is housed in a 24-lead Plastic Dual-In-Line Package (PDIP), JEDEC MS-001, 0.300" wide, with through-hole mounting and standard 0.1" pin pitch for prototyping and legacy PCB assembly.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| A1–A8 | Bus A I/O port | 8-bit bidirectional data interface for side A; functions as input during store, output during transfer |
| B1–B8 | Bus B I/O port | 8-bit bidirectional data interface for side B; same dual-role behavior as A port |
| CAB | Register A clock | Positive-edge-triggered load control for A-register; captures A-bus data on rising edge |
| CBA | Register B clock | Positive-edge-triggered load control for B-register; captures B-bus data on rising edge |
| SAB | Select A-to-B path | HIGH selects stored A data; LOW selects real-time A data - make-before-break prevents glitches |
| SBA | Select B-to-A path | HIGH selects stored B data; LOW selects real-time B data - synchronized with SAB logic |
| DIR | Direction control | When G = LOW: DIR = H enables A→B transfer; DIR = L enables B→A transfer |
| G | Output enable | LOW enables transceiver outputs; HIGH disables both A and B 3-STATE drivers while preserving inputs |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B registers | Enables asynchronous latching of data from two separate buses without cross-talk or timing conflict |
| Make-before-break select logic | Eliminates momentary bus disconnection during SAB/SBA transitions-critical for glitch-sensitive control lines |
| Totem-pole 3-STATE outputs | Drives bus capacitance up to 50 pF directly; removes need for external pull-up resistors or bus buffers |
| Four-mode operation control | Single device replaces discrete logic for bidirectional transfer, register load, isolation, and stored-output functions |
Applications
| Industrial Backplane Interface | Microprocessor System Bus Buffer |
|---|---|
Use Scenario: Interfacing multiple I/O modules to a shared 8-bit data bus in programmable logic controllers (PLCs). IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register hold capability to isolate modules during reconfiguration. Use Value: Enables hot-swap-safe data routing using stored register values while real-time bus remains active for diagnostics. | Use Scenario: Connecting Z80 or 8085 CPU address/data bus to peripheral memory or UART chips. IC Role / Device Role / Timing Role: Registered bus driver providing setup/hold timing compliance for memory read/write cycles. Use Value: Meets 10 ns data setup (tSU) and zero hold time (tH) requirements for 4 MHz CPU bus timing. |
| Legacy Test Equipment Data Path | Digital Signal Acquisition Front-End |
Use Scenario: Routing sensor data between ADC front-end and FPGA processing unit in benchtop analyzers. IC Role / Device Role / Timing Role: Multiplexed transceiver selecting between live sensor stream and pre-triggered snapshot buffer. Use Value: Make-before-break SAB/SBA switching ensures uninterrupted data flow during trigger event capture. | Use Scenario: Isolating digital control signals from analog acquisition circuitry in mixed-signal DAQ systems. IC Role / Device Role / Timing Role: 3-STATE-enabled isolation gate preventing noise coupling during ADC conversion windows. Use Value: G-controlled disable (tPHZ ≤ 10 ns) provides precise timing window for analog settling before sampling. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal 3-STATE bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS646N | Identical logic function, pinout, and DC specs; TI-manufactured version with same 24-pin PDIP package | No functional deviation; fully interchangeable in legacy designs where Fairchild sourcing is constrained | Preferred when TI's long-term availability or distribution channel alignment is prioritized |
| DM74ALS645N | Lacks internal registers and dual-clock inputs; only real-time bidirectional transfer (no stored-data mode) | Cannot replace DM74ALS646NT in applications requiring registered data hold or glitch-free multiplexing | Select only if design uses only real-time A↔B transfer and omits register functionality |
Compared with SN74ALS646N and DM74ALS645N, the DM74ALS646NT uniquely combines registered storage, dual-clock control, and make-before-break select logic-making it irreplaceable in systems requiring deterministic data capture and glitch-free bus arbitration.
Availability
DM74ALS646NT is available at Aetrix Electronics and suitable for industrial backplane interfaces, microprocessor system bus buffering, and legacy test equipment data path management requiring stable component supply across extended production lifecycles.
Supply support for DM74ALS646NT 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
Fairchild Semiconductor was a U.S.-based semiconductor company specializing in analog and mixed-signal ICs, acquired by ON Semiconductor in 2016. Known for high-reliability TTL and CMOS logic families.
The DM74ALS646NT belongs to Fairchild's advanced Schottky TTL (ALS) logic product line, engineered for high-speed, low-power bus interfacing in industrial and computing systems requiring robust noise immunity and direct bus drive capability.
FAQ
What is the maximum clock frequency supported by the DM74ALS646NT?
The DM74ALS646NT supports a maximum clock frequency of 40 MHz, as specified in its Electrical Characteristics table under fCLK. This rating applies across the full recommended operating temperature range (0°C to +70°C) and ensures reliable edge-triggered register capture for high-speed data latching in legacy microprocessor systems. The DM74ALS646NT achieves this performance using Fairchild's advanced oxide-isolated, ion-implanted Schottky TTL process.
Does the DM74ALS646NT require external pull-up resistors on its bus lines?
No, the DM74ALS646NT does not require external pull-up resistors. Its totem-pole 3-STATE outputs are designed to drive highly capacitive or low-impedance bus lines directly, providing sufficient HIGH-level drive (VOH ≥ 2.4 V at IOH = −3 mA) and LOW-level sink (IOL = 24 mA) to maintain valid logic levels without termination components. This feature is explicitly confirmed in the General Description section of the DM74ALS646NT datasheet.
How does the make-before-break logic work on the DM74ALS646NT's SAB and SBA pins?
The DM74ALS646NT implements make-before-break logic on SAB and SBA to prevent bus glitches during mode transitions: when switching between real-time and stored data paths, the new path is established before the old path is disconnected. This eliminates momentary high-impedance states that could cause undefined bus levels. The DM74ALS646NT datasheet confirms this behavior in the General Description and Function Table notes, specifying it as a core design feature for reliable multiplexer operation.
Can the DM74ALS646NT operate with a 3.3V supply voltage?
No, the DM74ALS646NT is not rated for 3.3V operation. Its Recommended Operating Conditions specify VCC = 5.0 V (min 5 V, max 5.5 V), and Absolute Maximum Ratings limit supply voltage to 7 V. Operation below 5 V violates specification and may result in unreliable register triggering, degraded noise margins, or failure to meet tSU/tH timing. For 3.3V systems, a level-shifting interface or modern 3.3V-compatible transceiver must be used instead of the DM74ALS646NT.
What is the thermal resistance (θJA) of the DM74ALS646NT in its PDIP package?
The DM74ALS646NT in its 24-lead PDIP package (N24C) has a typical junction-to-ambient thermal resistance (θJA) of 44.5°C/W, as stated in the Absolute Maximum Ratings table. This value reflects standard JEDEC test conditions (still air, single-layer board) and is critical for calculating junction temperature rise under load. Designers must ensure power dissipation (ICC × VCC) stays within limits to maintain operation within the 0°C to +70°C free-air temperature range specified for the DM74ALS646NT.
DM74ALS646NT Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74ALS
- Package/Case:
- 24-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Logic Type:
- Transceiver, Non-Inverting
- Number of Elements:
- 1
- Number of Bits per Element:
- 8
- Input Type:
- -
- Output Type:
- 3-State
- Current - Output High, Low:
- 15mA, 24mA
- Voltage - Supply:
- 4.5V ~ 5.5V
- Operating Temperature:
- 0°C ~ 70°C (TA)
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 24-PDIP
DM74ALS646NT FAQ
1.How can I place an order for DM74ALS646NT through Aetrix?
Please submit a Request for Quotation (RFQ) for DM74ALS646NT 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 DM74ALS646NT reliable?
The price and inventory of DM74ALS646NT are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for DM74ALS646NT is usually 5 days.
3.What payment methods are accepted for DM74ALS646NT?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for DM74ALS646NT transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for DM74ALS646NT?
DM74ALS646NT orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your DM74ALS646NT 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 DM74ALS646NT?
For technical support, including DM74ALS646NT datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your DM74ALS646NT requirements.
6.How does Aetrix verify that DM74ALS646NT is sourced from the original manufacturer or authorized distributors?
All DM74ALS646NT 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 DM74ALS646NT meets industry standards.
7.What is the process for return or replacement of DM74ALS646NT?
All DM74ALS646NT units undergo pre-shipment inspection (PSI). If there is an issue with DM74ALS646NT, 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 DM74ALS646NT part is unused and in its original packaging.
Return procedure for DM74ALS646NT:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
DM74ALS646NT Tags
-
SN74LVC1G17DBVR
Texas Instruments
-
SN74LVC1G07DCKR
Texas Instruments
-
SN74LVC1G17DCKR
Texas Instruments
-
SN74LVC1G07DBVR
Texas Instruments
-
SN74LVC1G125DCKR
Texas Instruments
-
SN74AHCT1G126DBVR
Texas Instruments
-
SN74LVC1G125DBVR
Texas Instruments
-
SN74AHCT1G125DBVR
Texas Instruments
-
SN74LVC2G17DBVR
Texas Instruments
-
SN74LVC2G07DCKR
Texas Instruments
-
SN74LVC1G34DCKR
Texas Instruments
-
SN74LVC2G17DCKR
Texas Instruments
Tech Hub
Counterfeit components can hide behind convincing markings and passing basic function tests. This engineering reference covers source traceability, external inspection, X-ray, XRF, electrical testing, …
A practical engineering and sourcing framework covering lifecycle verification, lifetime-buy calculations, replacement qualification, supplier checks and counterfeit-risk controls.
TTL and CMOS logic families differ in thresholds, loading, output drive, power and timing. This engineering guide compares 74HC and 74HCT, calculates noise margins and checks 3.3 V/5 V compatibility.
A practical engineering guide to 3.3V and 5V logic compatibility, input thresholds, resistor dividers, translator ICs, MOSFET level shifting, I2C pull-ups, timing limits and power-sequencing risks.
The 74HC595 uses push-pull logic outputs, while the TPIC6B595 uses 50 V open-drain DMOS sinks for higher-power loads. This guide compares timing, current limits, 3.3 V interfacing, load wiring, thermal…
The 74HC595 converts serial data into eight stable parallel outputs. This guide covers pin functions, shift and storage timing, OE and MR behavior, drive-current limits, cascading, voltage compatibilit…
A technical comparison of level-sensitive latches and edge-triggered flip-flops, covering timing windows, setup and hold limits, master–slave operation, time borrowing, race-through, HDL inference and…
A D latch stores one bit while Enable controls when data can pass. This reference covers gate-level operation, truth tables, transparency, setup and hold timing, LE versus OE, common ICs and practical …
An SR latch stores one bit through cross-coupled feedback. This engineering reference covers NOR and NAND implementations, truth tables, forbidden-state recovery, gated operation, switch debouncing, fa…
Latch circuits retain one bit through feedback. This technical reference covers SR and D latches, truth tables, transparency, timing limits, latch-versus-flip-flop behavior, applications and common log…
