Renesas 728985JG8

Overview

IDT728985JG8 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 - deployed in voice/data TDM switching systems requiring per-channel variable or constant throughput delay.

For engineers reviewing the IDT728985JG8 datasheet, IDT728985JG8 pinout, IDT728985JG8 application, or IDT728985JG8 equivalent, key selection criteria include ST-BUS®/GCI auto-detection capability, microprocessor-controlled connection memory (HIGH/LOW), frame integrity support in Constant Delay mode, and PLCC-44 packaging with three-state TX outputs.

Technical Context

The IDT728985JG8 implements a dual-mode TSI architecture: Variable Delay mode delivers minimum 3-slot latency for voice paths, while Constant Delay mode guarantees frame-aligned 32–94 slot delays using multi-buffered Data Memory. It integrates automatic ST-BUS®/GCI format and polarity detection on F0i/C4i inputs.

Its 8-bit non-multiplexed microprocessor interface (A0–A5, D0–D7, CS, DS, R/W, DTA) enables real-time read/write access to Control Register, Connection Memory HIGH/LOW, and read-only Data Memory - with DTA acknowledgment delays up to 1220 ns for Data Memory reads.

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 ISL3036IRZ and uPD720101GC-80, the IDT728985JG8 uniquely combines PLCC-44 packaging, 5 V single-supply operation, ST-BUS®/GCI auto-detection, and dual delay modes - making it the only drop-in replacement for legacy telecom equipment requiring mechanical and electrical backward compatibility.

Availability

IDT728985JG8 is available at Aetrix Electronics and suitable for ISDN PRI gateways, TDM voice switching matrices, PCM multiplexers, and telecom backplane interconnects requiring stable component supply and long-term industrial temperature support.

Supply support for IDT728985JG8 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.

The IDT728985 belongs to IDT's legacy TSI product line designed specifically for carrier-grade telecommunication infrastructure - emphasizing deterministic latency, protocol flexibility, and microprocessor configurability in E1/T1 switching applications.

FAQ

What is the primary function of the IDT728985JG8 in a telecom system?

The IDT728985JG8 serves as a 256 × 256 time slot interchange digital switch that routes individual 64 Kbit/s PCM time slots between eight serial input (RX0–RX7) and eight serial output (TX0–TX7) streams. It enables non-blocking, microprocessor-configurable TDM switching in ST-BUS®/GCI-compliant systems such as ISDN PRI gateways and voice switching matrices. Its role is to maintain precise time slot alignment while supporting both voice-optimized (Variable Delay) and data-integrity (Constant Delay) operational modes - all implemented within the IDT728985JG8 silicon.

Does the IDT728985JG8 support both ST-BUS® and GCI protocols simultaneously?

Yes, the IDT728985JG8 features hardware-based automatic protocol identification on its F0i frame sync and C4i clock inputs. It detects whether the incoming signal conforms to ST-BUS® (active-LOW frame pulse) or GCI (active-HIGH frame pulse) specifications and configures internal timing edges accordingly - without requiring external configuration or firmware intervention. This dual-protocol support is intrinsic to the IDT728985JG8 design and enables seamless integration into heterogeneous telecom backplanes.

What are the key timing differences between Variable and Constant Delay modes in the IDT728985JG8?

In Variable Delay mode, the IDT728985JG8 achieves minimum 3-slot latency (e.g., input channel n → output channel n+3), scaling linearly with channel offset. In Constant Delay mode, all paths exhibit fixed frame-aligned delays: minimum 32 slots (input ch32 → output ch1) and maximum 94 slots (input ch1 → output ch32), calculated as DELAY = [32 + (32 − IN) + (OUT − 1)]. This guarantee ensures inter-channel timing integrity for grouped data services - a behavior hardwired into the IDT728985JG8's multi-buffered Data Memory architecture.

How does the microprocessor interface of the IDT728985JG8 handle memory access conflicts?

The IDT728985JG8 uses time-multiplexed arbitration between TDM port accesses and microprocessor (MPU) operations. The DTA (Data Acknowledgment) signal indicates completion of each MPU read/write, with acknowledgment delays ranging from 40 ns (Control Register) to 1220 ns (Data Memory reads). The Split Memory (SM) bit in the Control Register allows concurrent MPU reads from Data Memory and writes to Connection Memory LOW - resolving contention by separating access domains. This behavior is documented in the IDT728985JG8 functional specification and timing tables.

What is the purpose of the CCO pin on the IDT728985JG8, and how is it used?

The CCO (Control Channel Output) pin on the IDT728985JG8 is a 2.048 Mb/s serial output carrying 256 bits per frame, where each bit corresponds to the CCO bit in one location of Connection Memory HIGH. It provides an auxiliary control channel synchronized to the TX streams - for example, transmitting per-channel enable states or status flags alongside payload data. The IDT728985JG8 outputs CCO bits one time slot ahead of their associated TX channel to accommodate external logic delays, ensuring deterministic timing alignment in systems using the IDT728985JG8.