NXP Semiconductors 74HCT670D,652

Overview

74HCT670D,652 from NXP Semiconductors is a 4×4 3-state register file IC used for simultaneous read/write data buffering in synchronous digital systems. It features independent read/write address inputs (RA/RB, WA/WB), active-low WE/RE controls, four bidirectional data lines (D0–D3/Q0–Q3), and operates at 4.5 V with 27 ns typical Dn→Qn propagation delay and 18 ns RE→Qn enable time.

For engineers reviewing the 74HCT670D,652 datasheet, 74HCT670D,652 pinout, 74HCT670D,652 application, or 74HCT670D,652 equivalent, key selection criteria include simultaneous read/write capability, 3-state bus-driving outputs, TTL-compatible input thresholds, 16-pin SOIC package constraints, and timing margins for latch-to-read sequencing in multi-register file stacks.

Technical Context

The 74HCT670D,652 implements a 16-bit register file organized as four 4-bit words, with physically separate read and write address decoders enabling concurrent access to different locations. Its dual-address architecture supports pipelined data flow where one word is written while another is read without contention.

It uses HCT-series CMOS technology with TTL-level input compatibility (VIH = 2.0 V min, VIL = 0.8 V max at VCC = 4.5 V), 3-state output drivers capable of bus loading, and internal latching synchronized to WE transitions - requiring stable WA/WB and Dn during WE low, with tlatch = 25 ns (typ) from WE↓ to next RA/RB↑.

Key Specifications

Pinout & Package

74HCT670D,652 is housed in a 16-pin small outline integrated circuit (SO16) package with standard JEDEC MS-012AC dimensions (10.0 mm × 4.4 mm, 1.27 mm pitch).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar register file applications.

Compared with 74HCT670D,652, the 74HC670D,653 offers wider voltage operation but lacks TTL input compatibility, while the SN74ALS670N delivers raw speed and legacy fit but sacrifices 3-state bus sharing and modern packaging - making 74HCT670D,652 optimal for new designs needing robust 5 V bus interfacing with expandable register architecture.

Availability

74HCT670D,652 is available at Aetrix Electronics and suitable for microcontroller data buffering, digital signal processing pipelines, industrial PLC I/O mapping, and legacy bus interface bridges requiring stable component supply and long-term lifecycle assurance.

Supply support for 74HCT670D,652 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

NXP Semiconductors is a global semiconductor leader focused on secure connectivity solutions for automotive, industrial, and IoT applications, with roots in Philips' pioneering logic IC development.

The 74HCT670D,652 belongs to NXP's legacy 74HCT logic family, designed specifically to provide TTL-compatible, low-power CMOS alternatives for register-intensive digital control systems requiring deterministic timing and bus-sharing capability.

FAQ

What is the maximum operating temperature range for the 74HCT670D,652?

The 74HCT670D,652 is rated for industrial operation from −40 °C to +85 °C, as confirmed in its AC characteristics table for 74HCT under Tamb = −40 to +85 °C conditions. This range applies to all timing parameters including propagation delays, setup/hold times, and 3-state enable/disable specifications. The device remains functional up to +125 °C in limited parameter mode but full specification compliance is guaranteed only within the −40 °C to +85 °C range. Always verify thermal derating in high-density PCB layouts.

Does the 74HCT670D,652 support true simultaneous read and write to the same register location?

No, the 74HCT670D,652 does not support simultaneous read and write to the same 4-bit word. Its architecture permits concurrent access only to *different* locations - e.g., writing to word 0 while reading from word 2. Attempting to read from a location while WE is LOW and WA/WB point to that same location results in indeterminate Qn output due to internal bus contention, as stated in the functional description: "The addressed location remains transparent to the data while the WE input is LOW." Safe operation requires tlatch = 25 ns minimum delay from WE↓ to subsequent RA/RB↑ for the same address.

What is the recommended minimum pulse width for the WE input on the 74HCT670D,652?

The 74HCT670D,652 requires a minimum WE LOW pulse width of 18 ns at VCC = 4.5 V, as specified in the AC Characteristics table for 74HCT. This ensures reliable latching of D0–D3 data into the addressed register location. Shorter pulses risk incomplete capture or metastability. At VCC = 5.0 V, the minimum widens to 20 ns; design margins should include 1.5× this value (≥27 ns) to accommodate trace skew, driver rise/fall asymmetry, and temperature variation across the industrial range.

Can multiple 74HCT670D,652 devices be connected in parallel to create an 8-bit or wider register file?

Yes, multiple 74HCT670D,652 devices can be paralleled for wider word lengths: connect all RE, WE, RA, RB, WA, and WB lines in common, then wire D0–D3 and Q0–Q3 of each device to adjacent data bus bits (e.g., U1.Q0–Q3 = D0–D3, U2.Q0–Q3 = D4–D7). The 3-state outputs prevent contention, and the datasheet explicitly states this expansion method supports "n-bit words" via parallel enable/address driving. Ensure RE timing is staggered or buffered to avoid overlapping active outputs.

Is the 74HCT670D,652 pin-compatible with the 74LS670?

Yes, the 74HCT670D,652 is pin-compatible with the 74LS670, as confirmed in the General Description: "pin compatible with low power Schottky TTL (LSTTL)." All 16 pins - including D0–D3, Q0–Q3, RA/RB, WA/WB, RE, WE, VCC, and GND - occupy identical positions in the SO16 package. However, note that the 74HCT670D,652 draws significantly less quiescent current and has different AC timing; system-level timing validation is required despite mechanical and logical pin alignment.