Renesas 728980J

Overview

IDT728980J from Renesas Electronics (formerly IDT) is a 256 × 256 non-blocking time slot interchange (TSI) digital switch for ST-BUS®-compliant telecom systems. It supports eight 2.048 Mb/s serial input streams (RX0–RX7), eight 2.048 Mb/s output streams (TX0–TX7), microprocessor-controlled configuration via an 8-bit parallel bus, and operates from a single +5 V supply across –40°C to +85°C.

For engineers reviewing the IDT728980J datasheet, IDT728980J pinout, IDT728980J application, or IDT728980J equivalent, this device serves as a core TSI element in PCM-based circuit-switched voice/data infrastructure-requiring precise frame alignment (F0i), 4.096 MHz serial clock (C4i), per-channel connection memory control, and ODE-gated three-state TX outputs.

Technical Context

The IDT728980J implements dual-mode switching: Connection Mode routes data from Data Memory using addresses stored in Connection Memory LOW, while Processor Mode directly outputs Connection Memory LOW contents on TX streams. Internal serial-to-parallel and parallel-to-serial conversion enforces minimum 2-channel delay depending on RX/TX stream pairing (e.g., RX0→TX1 achieves minimal latency).

Control is managed through a 6-bit address bus (A0–A5), with A5 selecting between Control Register (A5=0) and 32-byte stream-specific memory pages (A5=1). The ODE pin globally enables/disables TX outputs, while individual channel enable (OE), source selection (CS), and CCO bit control reside in Connection Memory HIGH locations.

Key Specifications

Pinout & Package

Package: 44-pin Plastic Leaded Chip Carrier (PLCC, J44), 0.65 in × 0.65 in, 0.05 in pitch.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar time slot interchange applications.

Compared with MC145506FN and Si2404-GM, the IDT728980J uniquely combines full 256×256 non-blocking switching, native ST-BUS® timing (F0i/C4i), parallel microprocessor control, and per-channel CCO signaling-making it optimal for retrofitting or maintaining established telecom infrastructure requiring precise frame-synchronous operation.

Availability

IDT728980J is available at Aetrix Electronics and suitable for PCM-based digital loop carrier systems, ISDN primary rate interface equipment, and digital cross-connect systems requiring stable component supply and long-term lifecycle support.

Supply support for IDT728980J 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

Renesas Electronics Corporation is a global semiconductor leader delivering trusted embedded solutions for automotive, industrial, infrastructure, and IoT applications.

The IDT728980J belongs to Renesas' legacy IDT telecom timing and switching portfolio, designed specifically for ST-BUS®-based time-division multiplexing infrastructure requiring deterministic, low-latency channel switching.

FAQ

What is the primary function of the IDT728980J in a telecom system?

The IDT728980J functions as a 256 × 256 time slot interchange digital switch that dynamically reroutes 64 Kbit/s PCM voice/data channels between ST-BUS® serial streams. It enables non-blocking, frame-synchronous switching under microprocessor control-critical for digital loop carriers, ISDN PRI gateways, and TDM cross-connect systems where precise channel-level connectivity must be reconfigured in real time without service interruption.

How does the IDT728980J handle timing synchronization with other ST-BUS® devices?

The IDT728980J uses two dedicated timing inputs: F0i (8 kHz frame pulse) and C4i (4.096 MHz serial clock). These pins lock the device to the ST-BUS® standard frame structure (125 μs frames, 32 channels/frame), ensuring bit- and frame-level alignment with upstream/downstream ST-BUS® components. Internal counters and memory addressing are driven directly from these signals, eliminating need for internal PLLs or clock synthesis.

What is the role of the ODE pin on the IDT728980J, and why is it critical during power-up?

The ODE (Output Drive Enable) pin is a master enable for all TX0–TX7 serial outputs. When held LOW at power-up, it forces all outputs into high-impedance state-preventing bus contention before Connection Memory HIGH is initialized. This avoids hazardous conditions where unprogrammed outputs could drive conflicting logic levels on shared ST-BUS® backplanes, making ODE essential for safe system initialization and hot-swap readiness.

Can the IDT728980J operate in both hardware-directed and CPU-controlled switching modes?

Yes, the IDT728980J supports two distinct operational modes. In Connection Mode, the CPU writes source addresses to Connection Memory LOW, and the device automatically reads corresponding data from Data Memory for output-enabling hardware-accelerated routing. In Processor Mode, the CPU writes payload data directly to Connection Memory LOW, which is then streamed out on TX lines-ideal for injecting supervisory tones or signaling messages. Mode selection is controlled via the PE bit in the Control Register.

What does the CCO pin on the IDT728980J output, and how is it used in system design?

The CCO (Control Channel Output) pin outputs a 2.048 Mb/s serial stream containing 256 bits per frame, each bit sourced from the CCO bit in Connection Memory HIGH for the corresponding channel. It is transmitted one channel early relative to the TX streams and is used to carry per-channel control information-such as echo cancellation enable flags, channel status bits, or alarm indicators-alongside voice/data payloads in extended ST-BUS® implementations.