Analog Devices Inc./Maxim Integrated DS2251T-64-16

Overview

DS2251T-64-16 from Maxim Integrated is an 8051-compatible soft microcontroller module with 64kB nonvolatile SRAM, 16MHz crystal support, and permanently powered real-time clock (RTC) with 100th-second resolution. It executes full 8051 instruction set, provides 32 I/O pins, and supports in-system reprogramming for adaptive firmware updates in data logging and power-critical embedded systems.

For engineers reviewing the DS2251T-64-16 datasheet, DS2251T-64-16 pinout, DS2251T-64-16 application, or DS2251T-64-16 equivalent, key selection criteria include NV SRAM partitioning capability, lithium-backed RTC interrupt sources (INTA/INTB/INTP), power-fail warning (VPFW = 4.37V typ), stop-mode current (80µA), and byte-wide bus interface (BA13–BA0 / BD7–BD0) for external peripheral mapping.

Technical Context

The DS2251T-64-16 implements a non-multiplexed byte-wide address/data bus (BA13–BA0 + BD7–BD0) decoupled from the 8051's standard Port 0/Port 2 multiplexed bus, preserving all 32 parallel I/O pins for application use. Memory access is controlled via R/W strobe and peripheral enables PE3/PE4, which map to 16kB boundaries (8000h–BFFFh and C000h–FFFFh).

Its power management architecture integrates three voltage thresholds: VPFW (4.37V typ) triggers early-warning interrupt, VCCMIN (4.12V typ) initiates reset, and VLI switches to lithium backup - all monitored using an internal band-gap reference. The RTC derives timing from an onboard 32kHz crystal and delivers SQW (1024Hz programmable), INTA, INTB, and INTP outputs.

Key Specifications

Pinout & Package

DS2251T-64-16 uses a 72-pin SIMM package (4.25″ × 1.00″ × 0.25″) with gold-edge contacts, designed for vertical insertion into socketed motherboards. Pin layout follows JEDEC-standard 72-pin SIMM mechanical footprint.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar microcontroller-with-NV-memory applications.

Compared with DS2251T-32-16 and DS2251T-128-16, the DS2251T-64-16 offers optimal balance: sufficient NV SRAM for complex adaptive firmware and multi-day data logging, while maintaining compatibility with existing 72-pin SIMM footprints and power budgets.

Availability

DS2251T-64-16 is available at Aetrix Electronics and suitable for industrial data loggers, power quality monitors, and adaptive firmware nodes requiring stable component supply, long-term lifecycle assurance, and RoHS-compliant packaging.

Supply support for DS2251T-64-16 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

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and embedded security ICs for industrial, medical, and communications applications.

The DS2251T-64-16 belongs to Maxim's secure microcontroller family, engineered specifically for systems demanding nonvolatile program storage, autonomous RTC operation, and fail-safe power management in unattended environments.

FAQ

What is the maximum crystal frequency supported by the DS2251T-64-16?

The DS2251T-64-16 supports a maximum crystal frequency of 16MHz, as confirmed in the Ordering Information table and AC Characteristics section. This applies to both the internal oscillator driving the 8051 core and the RTC's 32kHz crystal - the latter being separate and fixed. Timing parameters such as tCLKHPW (15ns min high time) and tCLKLPW (15ns min low time) are specified at 16MHz operation, validating full-speed functionality for the DS2251T-64-16.

Does the DS2251T-64-16 require external pull-up resistors on Port 0?

Port 0 (P0.0–P0.7) of the DS2251T-64-16 functions as an open-drain bus and requires external pull-ups only when used as a general-purpose I/O port. However, when operating in expanded bus mode - where it serves as the multiplexed address/data bus - external pull-ups are not required, as stated in the PIN DESCRIPTION section. This dual behavior is inherent to the DS2251T-64-16's architecture and eliminates unnecessary components in memory-mapped configurations.

How does the DS2251T-64-16 handle power failure events?

The DS2251T-64-16 implements three-tiered power-fail response: (1) VPFW = 4.37V (typ) triggers an early-warning interrupt at vector 2Bh; (2) VCCMIN = 4.12V (typ) forces hardware reset; (3) VLI threshold switches to lithium backup, asserting PF = 0. All nonvolatile resources - including 64kB NV SRAM and RTC state - remain intact for ≥10 years at room temperature with no VCC, per the DS2251T-64-16 datasheet specifications.

Can the DS2251T-64-16 be programmed in-system without external hardware?

Yes - the DS2251T-64-16 includes an on-chip serial Bootstrap loader activated by a falling edge on the PROG pin. This allows full in-system programming via its UART (P3.0/RXD and P3.1/TXD), eliminating need for external programmers. The loader validates software integrity (e.g., CRC-16) before execution and becomes transparent post-load, enabling field firmware upgrades directly through the DS2251T-64-16's serial interface.

What is the purpose of the PE3 and PE4 pins on the DS2251T-64-16?

PE3 and PE4 are peripheral enable outputs on the DS2251T-64-16 that decode 16kB memory regions: PE3 asserts for addresses 8000h–BFFFh, and PE4 for C000h–FFFFh. These signals are not lithium-backed, allowing safe connection to volatile peripherals. They work in conjunction with the byte-wide bus (BA13–BA0 / BD7–BD0) and R/W to enable memory-mapped I/O without consuming any of the 32 general-purpose I/O pins - a defining architectural feature of the DS2251T-64-16.