Analog Devices Inc./Maxim Integrated DS21FT40N

Overview

DS21FT40 from Dallas Semiconductor (now Maxim Integrated) is a 12-channel E1 framer multi-chip module integrating three DS21Q44 quad-framer die in a single 27 mm × 27 mm BGA package. It supports FAS, CAS, CCS, and CRC4 framing formats, provides dual two-frame elastic stores per framer, and operates at 3.3 V with 5 V–tolerant I/O for telecom line interface applications.

For engineers reviewing the DS21FT40 datasheet, DS21FT40 pinout, DS21FT40 application, or DS21FT40 equivalent, key selection criteria include E1 channel density, independent framer operation, elastic store support for asynchronous backplane interfacing up to 8.192 MHz, IEEE 1149.1 testability, and compatibility with ITU-T G.704/G.706/G.962 and ETSI 300 011/300 233 standards.

Technical Context

The DS21FT40 implements twelve fully independent E1 framers-four per DS21Q44 die-with no shared framing synchronizer. Each framer's transmit and receive paths operate with separate clocks, enabling asynchronous backplane integration via RSYSCLK/TSYSCLK inputs supporting burst rates up to 8.192 MHz.

Each framer includes an integral HDLC controller with 64-byte buffers configurable for Sa-bit or DS0 operation, plus hardware signaling extraction/insertion, AIS/remote alarm detection/generation, and large error counters for BPV, CRC4, FAS, and E-bits aligned to ITU-T and ETSI requirements.

Key Specifications

Pinout & Package

DS21FT40 uses a 300-pin, 1.27 mm pitch ball grid array (BGA) package measuring 27 mm × 27 mm. The package integrates three DS21Q44 quad-framer die with dedicated power/ground pins per framer group (DVDD1/DVSS1 through DVDD3/DVSS3), 12-channel differential receive/transmit data paths (RPOS/RNEG/RSER/TPOS/TNEG/TSER), and independent clock/sync resources per framer (RCLK/RSYSCLK/RSYNC/RMSYNC and TCLK/TSYSCLK/TSYNC/TSSYNC).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar E1 framer applications.

Compared with DS21FT44 and DS21Q44, the DS21FT40 uniquely delivers 12-channel density with per-framer RMSYNC outputs and separated RSYSCLK/TSYSCLK domains-enabling deterministic CAS-aligned multiframe distribution across high-port-count telecom platforms without layout-level timing compromises.

Availability

DS21FT40 is available at Aetrix Electronics and suitable for telecom infrastructure, base station line cards, and DSLAM aggregation modules requiring stable component supply and long-term lifecycle support.

Supply support for DS21FT40 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

Dallas Semiconductor, now part of Maxim Integrated, specializes in precision analog, mixed-signal, and timing ICs for communications, industrial, and computing markets.

The DS21FT40 belongs to Maxim's E1/T1 framer product line, engineered specifically for high-density, low-power telecom line interface applications demanding full ITU-T/ETSI compliance and multiframe signaling integrity.

FAQ

What is the primary function of the DS21FT40 in a telecom system?

The DS21FT40 serves as a 12-channel E1 framer multi-chip module that performs frame alignment, multiframe synchronization, CAS/CCS signaling extraction and insertion, and elastic store–based clock domain bridging. Its role is to condition and adapt E1 data streams for transport across asynchronous backplanes while maintaining strict ITU-T G.704/G.706 timing and signaling integrity-making it essential in base station line cards and DSLAM aggregation modules where DS21FT40 handles all physical layer framing tasks independently per channel.

How does the DS21FT40 differ from the DS21FT44?

The DS21FT40 separates RSYSCLK and TSYSCLK pins per framer, adds RMSYNC outputs for multiframe boundary distribution, ties FMS to Vdd, and removes JTAG (JTRST*/JTMS/JTCLK/JTDI/JTDO) and RSIG/TSIG pins. In contrast, DS21FT44 retains integrated JTAG and analog signaling interfaces but lacks RMSYNC and split system clock routing. These differences make DS21FT40 optimal for CAS-aligned multiframe distribution, while DS21FT44 suits debug-intensive or legacy signaling environments-both share identical framer logic and register maps except for these pin-level distinctions.

Does the DS21FT40 support CRC4 and CAS multiframe formats?

Yes, the DS21FT40 fully supports both CRC4 and CAS multiframe formats per ITU-T G.704 and ETSI 300 011. It extracts and inserts CAS signaling bits, detects CRC4 code word errors, and provides RMSYNC outputs synchronized to CRC4 multiframe boundaries. The device also supports FAS and CCS formats, with configurable registers allowing runtime switching between multiframe types on a per-framer basis-ensuring DS21FT40 interoperability across European (CRC4) and legacy (CAS) E1 network deployments.

What is the purpose of the RMSYNC pins on the DS21FT40?

The RMSYNC pins (RMSYNC1–RMSYNC12) output a 1-RSYSCLK-wide pulse marking CRC4 multiframe boundaries for each of the 12 framers. This signal enables precise hardware-level synchronization of CAS signaling operations across multiple framers or external devices, eliminating software polling or timing-critical CPU intervention. In systems using DS21FT40 for trunk-side E1 aggregation, RMSYNC ensures deterministic alignment of channel-associated bit extraction/insertion-critical for SS7 or ISDN Q.931 call control signaling integrity.

Can the DS21FT40 operate without external elastic store circuitry?

Yes-the DS21FT40 integrates dual two-frame elastic stores within each framer, eliminating the need for external FIFOs or buffer ICs. When enabled, these elastic stores absorb phase and frequency differences between the recovered 2.048 MHz E1 clock and an asynchronous backplane clock (up to 8.192 MHz) applied to RSYSCLK/TSYSCLK. The DS21FT40 manages slip buffer control autonomously via internal logic, making external elastic store circuitry unnecessary-reducing BOM cost and PCB complexity while maintaining DS21FT40's full compliance with ITU-T G.706 slip performance requirements.