Renesas 728985JG

Overview

IDT728985JG from Integrated Device Technology is a 256 × 256 non-blocking time slot interchange (TSI) digital switch IC for ST-BUS®/GCI telecommunication backplanes, supporting 8 RX and 8 TX serial streams at 2.048 Mb/s, 5 V supply, and −40°C to +85°C operation in PLCC-44 package.

For engineers reviewing the IDT728985JG datasheet, IDT728985JG pinout, IDT728985JG application, or IDT728985JG equivalent, key selection considerations include per-channel variable/constant throughput delay mode selection, microprocessor-controlled connection memory access (A0–A5, D0–D7, CS/DS/R/W), frame integrity support for PCM/data networks, and ST-BUS®/GCI auto-detection via F0i/C4i inputs.

Technical Context

The IDT728985JG implements a dual-mode TSI architecture with independent Connection Memory High (CMH) and Connection Memory Low (CML) for per-channel switching control. It supports both Connection Mode (data routed from Data Memory based on CML addresses) and Processor Mode (data written directly to CML by host CPU).

Its timing unit automatically detects ST-BUS® (active-low frame sync) or GCI (active-high frame sync) formats using F0i and C4i inputs, then configures internal sampling edges accordingly. Variable Delay mode achieves minimum 3-slot latency; Constant Delay mode guarantees frame-aligned 32–94 slot delays using multi-buffered Data Memory.

Key Specifications

Pinout & Package

Package: 44-pin Plastic Leaded Chip Carrier (PLCC, J44-1), 0.05 in pitch, 0.65 in × 0.65 in footprint, lead-free (Green) variant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT728985JG, the IDT72V2115L15PF offers lower power and voltage but sacrifices scalability and telecom-specific features, while the NB7L14M provides raw bandwidth without time-slot awareness - neither supports the IDT728985JG's frame-aligned 256×256 switching, auto-format detection, or guaranteed minimum/maximum delay guarantees essential for E1 infrastructure.

Availability

IDT728985JG is available at Aetrix Electronics and suitable for ISDN PRI gateways, TDM multiplexers, VoIP media gateways, and legacy PBX digital trunk interfaces requiring stable component supply across long-lifecycle telecom deployments.

Supply support for IDT728985JG 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

Integrated Device Technology (IDT), now part of Renesas Electronics, is a fabless semiconductor company specializing in timing, memory interface, RF, and high-performance interconnect solutions for communications and computing markets.

IDT728985JG belongs to IDT's Time Slot Interchange product line, designed specifically for carrier-grade TDM switching in E1/T1 infrastructure, supporting ST-BUS® and GCI protocols with deterministic latency and frame integrity.

FAQ

What is the primary function of the IDT728985JG in a telecommunications system?

The IDT728985JG serves as a 256 × 256 time slot interchange digital switch that dynamically routes individual 64 kbit/s PCM time slots between eight input (RX0–RX7) and eight output (TX0–TX7) serial streams. It enables non-blocking circuit-switched connections in E1/T1 infrastructure, supporting both Connection Mode (hardware-directed routing) and Processor Mode (CPU-programmed data injection), making it essential for ISDN PRI gateways, TDM multiplexers, and digital trunk interfaces where precise time-slot manipulation is required.

Does the IDT728985JG support both ST-BUS® and GCI interface standards?

Yes, the IDT728985JG incorporates automatic interface detection via its F0i frame sync input and C4i clock input. It senses whether the incoming frame pulse is active-high (GCI) or active-low (ST-BUS®) and internally configures its serial timing unit accordingly - including bit sampling edges and frame boundary alignment - eliminating the need for external configuration or mode pins. This dual-standard support is confirmed in the functional description and timing diagrams (Figures 7 and 8) of the official datasheet.

What are the two throughput delay modes supported by the IDT728985JG, and how do they differ?

The IDT728985JG supports Variable Delay mode (minimum 3 time slots, up to 34 slots) and Constant Delay mode (32–94 time slots). In Variable Delay mode, latency depends solely on input–output time slot offset, optimizing for voice where low latency is critical. In Constant Delay mode, all switched data maintains fixed frame alignment - input frame N always appears on output frame N+2 - ensuring inter-channel timing integrity for data services like ISDN B-channel bonding or ATM cell assembly. Both modes are selectable per channel via bit 6 (V/C) in Connection Memory High.

How does the microprocessor interface of the IDT728985JG operate, and what signals are required?

The IDT728985JG uses a non-multiplexed 8-bit parallel interface with six address lines (A0–A5), eight data lines (D0–D7), and four control signals: CS (chip select, active-low), DS (data strobe, active-high), R/W (read/write direction), and DTA (data acknowledge, open-drain active-low). This Motorola-compatible bus allows direct connection to 8051, Z80, or similar microcontrollers. The DTA signal indicates transfer completion, with acknowledgment delays ranging from 40 ns (control register) to 1220 ns (Data Memory reads), as specified in the timing tables.

What package type is used for the IDT728985JG, and is it RoHS-compliant?

The IDT728985JG is packaged in a 44-pin Plastic Leaded Chip Carrier (PLCC, order code J) with 0.05 inch pitch and 0.65 inch × 0.65 inch body size (J44-1). Per the ordering information on page 13 of the datasheet, the "JG" suffix denotes the green (lead-free/RoHS-compliant) version. This is confirmed by the package documentation reference PSC4008.pdf and the explicit labeling "Green Plastic Leaded Chip Carrier" in the part number decoding table.