Analog Devices Inc./Maxim Integrated DS87C520-QNL

Overview

DS87C520-QNL from Maxim Integrated is a high-speed, 8051-compatible microcontroller with 16kB on-chip EPROM, 1kB MOVX-accessible SRAM, and 256 bytes of scratchpad RAM. It operates at up to 33MHz (121ns instruction cycle), features dual hardware serial ports, three 16-bit timer/counters, and supports industrial temperature range (–40°C to +85°C) in 44-pin PLCC package for embedded control in instrumentation and industrial automation.

For engineers reviewing the DS87C520-QNL datasheet, DS87C520-QNL pinout, DS87C520-QNL application, or DS87C520-QNL equivalent, key selection considerations include its 4-clock-per-machine-cycle architecture, ROMSIZE register for dynamic internal/external memory mapping, Power Management Mode for low-power operation, and dual data pointer support for accelerated block memory transfers.

Technical Context

The DS87C520-QNL implements a redesigned 8051 core executing instructions in 4 clocks per machine cycle-3× faster than standard 8051 at identical crystal frequency-enabling 82.5MHz apparent throughput at 33MHz clock. Its memory subsystem includes configurable ROMSIZE (0–16kB) and DME-controlled 1kB on-chip SRAM accessible via MOVX, both dynamically adjustable in runtime.

Hardware peripherals include two full-duplex UARTs (P3.0/P3.1 and P1.2/P1.3), six external interrupts (INT0–INT5), programmable watchdog timer, power-fail reset, and early-warning power-fail interrupt. The Power Management Mode selects CPU clock division by 64 or 1024, reducing machine cycle rate to 187.5kHz or 11.7kHz at 12MHz crystal, with automatic hardware/software exit.

Key Specifications

Pinout & Package

DS87C520-QNL is housed in a 44-pin Plastic Leaded Chip Carrier (PLCC) package with 0.6-inch body size, lead-free/RoHS-compliant construction, and thermal characteristics suitable for industrial ambient conditions.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 8051-compatible microcontroller applications.

Compared with DS87C520-QNL, DS83C520-QNL offers identical performance and packaging but eliminates EPROM reprogrammability for lower cost, while AT89C51RD2-RLT provides greater Flash capacity at the expense of architectural speed enhancements and memory flexibility.

Availability

DS87C520-QNL is available at Aetrix Electronics and suitable for industrial automation, medical device control, smart metering, and automated test equipment requiring stable component supply across extended temperature ranges and long product lifecycles.

Supply support for DS87C520-QNL 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 high-reliability semiconductor solutions for industrial, medical, and communications markets.

The DS87C520-QNL belongs to Maxim's high-speed 8051 microcontroller product line, engineered for deterministic real-time control in resource-constrained embedded systems where legacy code compatibility, power efficiency, and memory flexibility are critical.

FAQ

What is the maximum operating frequency of the DS87C520-QNL?

The DS87C520-QNL supports a maximum crystal frequency of 33MHz, delivering a 121ns single-cycle instruction execution time. This corresponds to an effective processing throughput of approximately 82.5MHz due to its 4-clock-per-machine-cycle architecture-2.5× faster than standard 8051 cores at the same crystal speed. The DS87C520-QNL maintains full functionality across its specified industrial temperature range (–40°C to +85°C) at this speed.

How does the ROMSIZE feature work in the DS87C520-QNL?

The ROMSIZE feature in the DS87C520-QNL uses bits RMS2–RMS0 in SFR location C2h to dynamically configure the upper boundary of on-chip program memory, selectable from 0kB to 16kB in powers of two. This allows runtime overlay of external Flash or ROM at addresses normally occupied by internal EPROM-enabling field firmware updates without hardware changes. The DS87C520-QNL defaults to 16kB on reset, and changing ROMSIZE requires timed-access writes to avoid code misalignment during execution.

Does the DS87C520-QNL support both internal and external data memory simultaneously?

Yes, the DS87C520-QNL supports concurrent internal and external data memory access through software-controlled configuration. Its 1kB on-chip SRAM (address 0000h–03FFh) is accessed via MOVX when enabled by DME1/DME0 bits in PMR (C4h); addresses above 03FFh automatically route to external memory via Ports 0 and 2. The DS87C520-QNL allows transparent switching between internal SRAM and external peripherals without memory remapping or address decoding logic.

What are the power-saving capabilities of the DS87C520-QNL?

The DS87C520-QNL implements Power Management Mode (PMM) that reduces CPU clock rate by factors of 64 or 1024 via software control of CD1/CD0 bits in PMR (C4h), lowering machine cycle rate to 187.5kHz or 11.7kHz at 12MHz crystal. This mode retains full peripheral operation-including UARTs, timers, and interrupts-with automatic hardware/software exit. The DS87C520-QNL also supports EMI reduction by disabling ALE output, further cutting dynamic power in noise-sensitive applications.

Can the DS87C520-QNL replace a standard 8051 in existing designs without modifications?

The DS87C520-QNL is pin-compatible and instruction-set compatible with standard 8051 devices in 44-pin PLCC packaging, allowing socket replacement in most cases. However, its 4-clock-per-cycle execution speeds up all instructions-requiring adjustment of timing-critical code (e.g., software delays, baud rate generators). The DS87C520-QNL maintains backward compatibility through default 12-clock timer operation, but full speed benefits require explicit configuration of timer control registers and verification of real-time constraints.