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onsemi DM74ALS646WMX
- Part No.:
- DM74ALS646WMX
- Manufacturer:
- onsemi
- Package:
- 24-SOIC (0.295", 7.50mm Width)
- Datasheet:
-
DM74ALS646WMX.pdf
- Description:
- IC TXRX NON-INVERT 5.5V 24SOP
- Quantity:
- Payment:
- Shipping:
Inventory:2,953
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Product details
Overview
DM74ALS646WMX from Fairchild Semiconductor is an octal 3-STATE bus transceiver and register IC with independent A/B registers, edge-triggered D-type flip-flops, real-time/stored data multiplexing, and totem-pole 3-STATE outputs rated for 24 mA sink and −15 mA source drive at 5 V. It operates from 0°C to +70°C and supports up to 40 MHz clock frequency in bus-organized systems such as industrial I/O controllers.
For engineers reviewing the DM74ALS646WMX datasheet, pinout, applications, or equivalent options, key selection criteria include its dual-register storage capability, make-before-break select logic, G/DIR-controlled four-mode operation, and direct bus-driving 3-STATE outputs without pull-ups.
Technical Context
The DM74ALS646WMX integrates two independent octal D-type registers clocked by separate CAB (A-register) and CBA (B-register) inputs, each triggered on the LOW-to-HIGH transition. Data routing is controlled by SAB/SBA select pins with "make before break" switching to prevent glitches during real-time ↔ stored data transitions.
Operation modes are defined by G (enable) and DIR (direction) pins: G = LOW enables bidirectional real-time or stored data transfer between A/B buses; G = HIGH disables outputs while preserving input functionality. All I/O ports remain active for storage regardless of G/DIR state.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| VCC Range | 5.0 V to 5.5 V - ensures compatibility with standard TTL logic supply rails |
| fCLK Max | 40 MHz - supports high-speed synchronous bus arbitration in legacy control systems |
| IOL / IOH | 24 mA sink / −15 mA source - drives capacitive bus loads directly without external buffers |
| tPLH / tPHL | 5–30 ns propagation delay - enables sub-25 ns timing margins in 20–25 MHz bus cycles |
| Operating Temp | 0°C to +70°C - qualified for commercial-grade industrial embedded applications |
| IOZH / IOZL | Included in IIH/IIL specs - eliminates need for separate high-impedance leakage characterization |
Pinout & Package
DM74ALS646WMX is housed in a 24-lead SOIC package (JEDEC MS-013, 0.300" wide, Package Number M24B), with gull-wing leads and 1.27 mm pitch.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| G | Output Enable | Active-LOW global 3-STATE control: HIGH disables A/B outputs but preserves input capture |
| DIR | Direction Control | When G = LOW, selects real-time A→B (DIR = HIGH) or B→A (DIR = LOW) data flow |
| CAB | A Register Clock | LOW-to-HIGH edge stores A-bus data into A register; independent of CBA |
| CBA | B Register Clock | LOW-to-HIGH edge stores B-bus data into B register; independent of CAB |
| SAB | A Bus Select | HIGH = route stored A data to B bus; LOW = route real-time A data to B bus |
| SBA | B Bus Select | HIGH = route stored B data to A bus; LOW = route real-time B data to A bus |
| A1–A8 | Data I/O Port A | Bidirectional TTL-compatible bus interface with 3-STATE output control |
| B1–B8 | Data I/O Port B | Bidirectional TTL-compatible bus interface with independent 3-STATE control |
Key Features
| Feature | Design Value |
|---|---|
| Independent A/B registers | Enables concurrent storage and forwarding of data from two separate buses without cross-talk |
| Make-before-break select logic | Eliminates output glitches during SAB/SBA transitions between real-time and stored data paths |
| Four-mode G/DIR control | Supports real-time A↔B transfer, A/B → storage, or stored → A/B - all in one device |
| Totem-pole 3-STATE outputs | Drives bus lines directly at 24 mA without pull-up resistors or interface logic |
Applications
| Industrial PLC I/O Module | Legacy Computer Backplane Interface |
|---|---|
Use Scenario: Isolating and buffering address/data buses between CPU and peripheral cards in ISA or VME backplanes. IC Role / Device Role / Timing Role: Bidirectional bus transceiver with register hold capability for pipeline staging and bus arbitration. Use Value: Eliminates need for discrete latches and direction-control logic, reducing component count by ≥3 per bus segment. | Use Scenario: Implementing programmable I/O ports in ladder-logic controllers with scan-cycle data retention. IC Role / Device Role / Timing Role: Dual-register buffer that captures sensor/actuator data on one clock edge and releases it on the next cycle. Use Value: Enables deterministic 1-cycle data latency between field I/O and CPU read/write operations. |
| Test Equipment Bus Controller | Avionics Maintenance Interface |
Use Scenario: Multiplexing multiple instrument data streams onto a shared GPIB or IEEE-488 bus. IC Role / Device Role / Timing Role: Real-time/stored data selector allowing simultaneous monitoring and logging without bus contention. Use Value: Supports glitch-free switching between live sensor feed and captured diagnostic snapshot during fault analysis. | Use Scenario: Interfacing ground-test equipment with legacy avionics LRUs using TTL-level parallel buses. IC Role / Device Role / Timing Role: Level-shifting, direction-controlled transceiver with storage for handshake synchronization across asynchronous subsystems. Use Value: Provides deterministic setup/hold timing (10 ns SU, 0 ns H) for reliable communication with flight-critical peripherals. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar octal bus transceiver and register applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| SN74ALS646N | Same logic function and pinout; PDIP-24 package (N24C), higher θJA (44.5°C/W vs 80.5°C/W) | Preferred for through-hole prototyping or legacy board rework where SOIC footprint unavailable | Select when manual soldering or socket-based testing required |
| DM74ALS645WMX | Omits B-register clock (CBA) and B-register storage; only A-register + transceiver mode | Reduces cost and complexity where unidirectional register+bus interface suffices | Choose when B-side storage is unnecessary and PCB space is constrained |
Compared with SN74ALS646N and DM74ALS645WMX, the DM74ALS646WMX uniquely supports full dual-register operation with independent CAB/CBA clocks and make-before-break select logic-critical for synchronized A/B bus arbitration in deterministic control systems.
Availability
DM74ALS646WMX is available at Aetrix Electronics and suitable for industrial PLC I/O modules, legacy computer backplane interfaces, and test equipment bus controllers requiring stable component supply over extended production lifecycles.
Supply support for DM74ALS646WMX 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 analog and mixed-signal semiconductor company, acquired by ON Semiconductor in 2016, known for high-reliability TTL, CMOS, and power management ICs.
The DM74ALS646WMX belongs to Fairchild's advanced Schottky TTL (ALS) logic family, designed specifically for high-speed, low-power bus interfacing in industrial control, instrumentation, and computing systems.
FAQ
What is the maximum clock frequency supported by the DM74ALS646WMX?
The DM74ALS646WMX supports a maximum clock frequency of 40 MHz, as specified in the Electrical Characteristics table under fCLK. This rating applies across the full recommended operating temperature range (0°C to +70°C) and with CL = 50 pF load. The device achieves this performance using Fairchild's advanced oxide-isolated, ion-implanted Schottky TTL process, enabling reliable high-speed register updates in synchronous bus systems.
Does the DM74ALS646WMX require external pull-up resistors on its 3-STATE outputs?
No, the DM74ALS646WMX does not require external pull-up resistors. Its totem-pole 3-STATE outputs provide sufficient HIGH-level drive (VOH ≥ 2.4 V at IOH = −3 mA) and high-impedance isolation to connect directly to bus lines. This design eliminates interface components and simplifies layout-confirmed by the General Description stating it can drive bus lines "without the need for interface or pull-up components."
How does the "make before break" behavior of SAB and SBA work in the DM74ALS646WMX?
The DM74ALS646WMX implements "make before break" on SAB and SBA by ensuring the newly selected data path (real-time or stored) is established before the prior path is disabled. This prevents momentary open-circuit or undefined states during transitions, eliminating glitches that would otherwise occur in typical multiplexers. The feature is explicitly documented in the General Description and verified in the Function Table timing relationships.
What are the thermal characteristics of the DM74ALS646WMX in its SOIC package?
The DM74ALS646WMX in the M24B SOIC package has a typical junction-to-ambient thermal resistance (θJA) of 80.5°C/W, as specified in the Absolute Maximum Ratings table. This value reflects standard JEDEC mounting conditions on a two-layer board with limited copper area. For sustained operation near maximum ICC (88 mA), derating or supplemental heat sinking may be required above ambient temperatures approaching 60°C.
Can the DM74ALS646WMX operate with a 3.3 V supply?
No, the DM74ALS646WMX is not rated for 3.3 V operation. Its Recommended Operating Conditions specify VCC = 5.0 V to 5.5 V, and Absolute Maximum Ratings limit supply voltage to 7 V. Electrical Characteristics-including VOH, VOL, and switching parameters-are guaranteed only within the 5 V TTL domain. Using 3.3 V will result in non-compliant output levels and unreliable register clocking.
DM74ALS646WMX Specifications
- Product attributes
- Attribute value
- Manufacturer:
- onsemi
- Series:
- 74ALS
- Package/Case:
- 24-SOIC (0.295", 7.50mm Width)
- Packaging:
- Tape & Reel (TR)
- 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:
- Surface Mount
- Supplier Device Package:
- 24-SOP
DM74ALS646WMX FAQ
1.How can I place an order for DM74ALS646WMX through Aetrix?
Please submit a Request for Quotation (RFQ) for DM74ALS646WMX 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 DM74ALS646WMX reliable?
The price and inventory of DM74ALS646WMX are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for DM74ALS646WMX is usually 5 days.
3.What payment methods are accepted for DM74ALS646WMX?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for DM74ALS646WMX transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for DM74ALS646WMX?
DM74ALS646WMX orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your DM74ALS646WMX 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 DM74ALS646WMX?
For technical support, including DM74ALS646WMX datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your DM74ALS646WMX requirements.
6.How does Aetrix verify that DM74ALS646WMX is sourced from the original manufacturer or authorized distributors?
All DM74ALS646WMX 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 DM74ALS646WMX meets industry standards.
7.What is the process for return or replacement of DM74ALS646WMX?
All DM74ALS646WMX units undergo pre-shipment inspection (PSI). If there is an issue with DM74ALS646WMX, 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 DM74ALS646WMX part is unused and in its original packaging.
Return procedure for DM74ALS646WMX:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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