Renesas 728981DBG

Overview

IDT728981DBG from Renesas Electronics is a 128 × 128 non-blocking time slot interchange (TSI) digital switch IC for ST-BUS®-compliant telecom systems. It supports four 2.048 Mb/s serial input streams (RX0–RX3), four 2.048 Mb/s serial output streams (TX0–TX3), 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 IDT728981DBG datasheet, IDT728981DBG pinout, IDT728981DBG application, or IDT728981DBG equivalent, key selection criteria include ST-BUS® frame alignment timing (tFPS/tFPH), per-channel connection memory control, ODE-driven three-state TX output management, and compatibility with 8 kHz frame-synchronized TDM infrastructure.

Technical Context

The IDT728981DBG implements dual-mode switching-Connection Mode (data routed from Data Memory using Connection Memory Low addresses) and Processor Mode (direct CPU-written data output)-with per-channel control via Connection Memory High bits. Its internal architecture includes on-chip serial-to-parallel and parallel-to-serial converters synchronized to a 4.096 MHz C4i clock and 8 kHz F0i frame pulse.

Switching latency varies by RX/TX stream pairing, with minimum delay of two channel slots (e.g., RX0→TX1/2/3, RX1→TX3); data cannot exit in the same time slot it enters due to required memory staging. The device uses Split Memory addressing (SM bit) and Stream Address bits (STA) to map A0–A5 accesses across Control Register, Data Memory, and Connection Memory LOW/HIGH subsections.

Key Specifications

Pinout & Package

Package: 44-pin Plastic Quad Flatpack (PQFP), DB44-1 footprint (10 mm × 10 mm, 0.80 mm pitch), green RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with IDT728981JG and IDT728981PG, the IDT728981DBG offers optimized thermal dissipation and signal integrity for high-density surface-mount telecom modules, with dedicated VCC/GND pins and PQFP lead geometry supporting automated assembly and EMI control.

Availability

IDT728981DBG is available at Aetrix Electronics and suitable for PCM multiplexers, digital cross-connect systems, ISDN PRI interfaces, and VoIP gateway TDM backplanes requiring stable component supply and long-term lifecycle support.

Supply support for IDT728981DBG 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 microcontrollers, analog, power, and connectivity solutions for automotive, industrial, and infrastructure markets.

The IDT728981DBG belongs to Renesas' legacy IDT time slot interchange product line, engineered specifically for ST-BUS®-based TDM switching in carrier-class telecom equipment and digital telephony systems.

FAQ

What is the primary function of the IDT728981DBG in a telecom system?

The IDT728981DBG serves as a 128 × 128 non-blocking time slot interchange digital switch, enabling dynamic, microprocessor-controlled routing of 64 kbit/s PCM channels across four 2.048 Mb/s ST-BUS® input and output streams. It performs serial-to-parallel conversion, memory-based time-slot mapping, and parallel-to-serial retransmission - all synchronized to 4.096 MHz and 8 kHz clocks. This makes the IDT728981DBG essential for TDM infrastructure like digital cross-connects and ISDN PRI gateways.

How does the IDT728981DBG handle frame synchronization and timing alignment?

The IDT728981DBG relies on two critical timing inputs: the 4.096 MHz C4i clock for serial data shifting and the 8 kHz F0i frame pulse for 125 μs boundary alignment. Internal counters reset on each F0i edge to ensure incoming serial data is correctly framed into 32-channel slots. All timing parameters - including tFPS (frame pulse setup), tFPH (hold), and tFPW (width) - are specified to guarantee zero-frame-slippage operation in ST-BUS®-compliant systems. The IDT728981DBG maintains this alignment even during clock pauses, though TX outputs enter high-impedance if C4i stops.

What are the differences between Connection Mode and Processor Mode in the IDT728981DBG?

In Connection Mode, the IDT728981DBG reads source addresses from Connection Memory LOW and fetches corresponding data from Data Memory for output - enabling hardware-routed time-slot switching. In Processor Mode (enabled by Control Register bit PE), the contents of Connection Memory LOW are output directly on TX streams - allowing CPU-driven data injection per channel. Both modes coexist per-channel via Connection Memory HIGH bit 2, and the IDT728981DBG supports Split Memory addressing to access both memories simultaneously during configuration.

Can the IDT728981DBG be used without a microprocessor interface?

No - the IDT728981DBG requires microprocessor initialization and runtime control. Its Control Register, Connection Memory, and Data Memory are only accessible via the 8-bit parallel bus (D0–D7, A0–A5, CS, DS, R/W). Power-up safety depends on the CPU asserting ODE = LOW first, then programming Connection Memory HIGH to prevent bus contention. While the serial streams operate autonomously once configured, all path setup, mode selection, and fault recovery depend on microprocessor interaction. The IDT728981DBG has no autonomous boot or configuration EEPROM.

What is the minimum achievable delay through the IDT728981DBG, and how is it determined?

The minimum delay through the IDT728981DBG is two channel slots (e.g., 125 μs × 2/32 ≈ 7.8 μs), achievable only with specific RX/TX stream pairings: RX0→TX1/TX2/TX3 and RX1→TX3. This delay arises because incoming data must be stored in Data Memory before being scheduled for output - preventing same-slot echo. The IDT728981DBG's internal memory queuing order and stream arbitration logic fix this latency; it cannot be reduced via configuration. Table 1 in the datasheet explicitly lists allowable combinations for minimum delay, and all other paths incur ≥3-slot delays.