Texas Instruments SN74ACT8997NT

Overview

SN74ACT8997NT from Texas Instruments is a JTAG TAP concatenator IC that links up to four secondary scan paths into a primary IEEE 1149.1 test bus, featuring an 8-bit programmable up/down counter, 4-bit hardwired ID bus, TTL-compatible inputs, and EPIC 1-µm CMOS process technology - used in high-reliability board-level test infrastructure for complex digital systems.

For engineers reviewing the SN74ACT8997NT datasheet, SN74ACT8997NT pinout, SN74ACT8997NT application, or SN74ACT8997NT equivalent, this device supports scan-path partitioning, dynamic SSP selection via instruction-controlled registers, boundary-scan register access, IRERR detection, and configurable DCO output behavior - all critical for JTAG-based system testability architecture design and debug.

Technical Context

The SN74ACT8997NT implements a fully IEEE Std 1149.1-compliant TAP controller with six stable states and synchronous operation (except counter) on TCK rising edge. It integrates six data registers - bypass (1-bit), control (10-bit), counter (8-bit), boundary-scan (10-bit), ID-bus (4-bit), and select (8-bit) - each accessible via dedicated instructions loaded into its 8-bit instruction register.

Scan-path configuration is determined by decoding the 8-bit select register and 10-bit control register, enabling per-SSP DTMS routing, DTDO activation, and DCO source/polarity/drive mode selection. The 4-bit ID bus is hardwired and scanned via the ID-bus register, while the 8-bit counter operates asynchronously to DCI transitions and supports up/down counting with latch-on-zero and IRERR-triggered interrupt output.

Key Specifications

Pinout & Package

SN74ACT8997NT is housed in a 300-mil 28-pin plastic dual in-line package (DIP), designated NT. Pin functions are electrically identical across DW, NT, and JT packages per TI SCAS157D datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar JTAG TAP concatenation applications.

Compared with SN74ACT8996NT and SN74ACT8998NT, the SN74ACT8997NT uniquely balances full IEEE 1149.1 compliance, 4-SSP support, integrated ID bus, and programmable counter - making it optimal for mid-complexity test architectures where identification and interrupt signaling are essential but eight-SSP scalability is not required.

Availability

SN74ACT8997NT is available at Aetrix Electronics and suitable for high-reliability PCB test infrastructure, modular system validation, and production-level JTAG diagnostics requiring stable component supply, long-lifecycle availability, and traceable sourcing.

Supply support for SN74ACT8997NT 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 global semiconductor leader specializing in analog, embedded processing, and connectivity technologies, with decades of leadership in testability and JTAG solutions.

The SN74ACT8997NT belongs to TI's SCOPE™ family of testability ICs, designed specifically to simplify IEEE 1149.1 implementation in complex digital systems by providing configurable scan-path linking, subsystem identification, and hardware-assisted test control.

FAQ

What is the operating temperature range for the SN74ACT8997NT?

The SN74ACT8997NT is rated for commercial operation from 0°C to +70°C. This specification applies specifically to the NT-package variant; military-grade SN54ACT8997 devices operate from –55°C to +125°C but use different packaging (JT/FK). The SN74ACT8997NT's thermal rating aligns with standard industrial board-level test environments and ensures stable TAP controller timing and register behavior across its full range.

Does the SN74ACT8997NT support both up-counting and down-counting modes?

Yes, the SN74ACT8997NT supports both up-counting and down-counting via bit 9 of its 10-bit control register. When bit 9 = 0, the 8-bit counter increments on each DCI transition; when bit 9 = 1, it decrements. The counter operates asynchronously to DCI and can be configured to latch at zero (down-count only) using bit 8 - enabling precise event-triggered interrupt generation through DCO for diagnostic or synchronization use cases.

How is the 4-bit ID bus used in the SN74ACT8997NT?

The 4-bit ID bus (ID1–ID4) in the SN74ACT8997NT is hardwired to external pull-up/pull-down resistors to encode a fixed subsystem identification code. That code is scanned out via the ID-bus register (a subset of the 10-bit boundary-scan register) during normal JTAG operations. This allows test software to automatically detect and differentiate between multiple SN74ACT8997NT-equipped modules in a daisy-chained JTAG system without requiring configuration registers or firmware.

Can the SN74ACT8997NT be bypassed in a JTAG scan chain?

Yes, the SN74ACT8997NT supports IEEE 1149.1 BYPASS instruction (0x81, 0x84, etc.), which places its 1-bit bypass register between TDI and TDO. In bypass mode, the device presents minimal delay and does not load or shift data through its internal registers. This allows the primary scan chain to route around the SN74ACT8997NT when secondary scan paths are inactive or during initialization sequences - preserving chain integrity and timing predictability.

What are the key differences between SN74ACT8997NT and SN74ACT8996NT?

The SN74ACT8997NT includes a 4-bit ID bus, 8-bit programmable counter with DCO interrupt output, and full 10-bit control register - features absent in the SN74ACT8996NT. The latter supports only basic 4-SSP selection and lacks ID bus, counter, and advanced DCO configuration. Therefore, SN74ACT8997NT is required when subsystem identification, event counting, or hardware-triggered diagnostics are needed - while SN74ACT8996NT suffices for simple scan-path concatenation only.