Analog Devices Inc./Maxim Integrated DS87C520-QCL+

Overview

DS87C520-QCL+ from Maxim Integrated is an 8051-compatible high-speed microcontroller with 16kB on-chip EPROM, 1kB MOVX-accessible SRAM, and 256 bytes of scratchpad RAM. It executes instructions in 4 clocks/machine cycle (vs. 12 for standard 8051), achieving 33MHz max clock rate and 121ns single-cycle instruction time. It serves as a drop-in upgrade in industrial control and embedded instrumentation requiring deterministic timing and dual serial port support.

For engineers reviewing the DS87C520-QCL+ datasheet, DS87C520-QCL+ pinout, DS87C520-QCL+ application, or DS87C520-QCL+ equivalent, key selection considerations include its PLCC-44 package compatibility with legacy 8051 sockets, ROMSIZE register programmability for boot block management, dual data pointer acceleration of memory moves, and Power Management Mode enabling 11.7kHz–3MHz machine cycle rates for portable systems.

Technical Context

The DS87C520-QCL+ implements a redesigned 8051 core eliminating dummy memory cycles, delivering 2.5× average speedup over standard 8051 at identical crystal frequency. Its architecture supports four-clock-per-cycle execution while retaining full 8051 instruction set and SFR compatibility-including new registers like ROMSIZE (C2h) and PMR (C4h) for memory mapping and power control.

It integrates two full-duplex hardware serial ports (UART0 and UART1), three 16-bit timer/counters (with optional 4-clock operation), programmable watchdog timer, power-fail reset, and early-warning interrupt. The dual DPTR (DPTR0 at 82h/83h, DPTR1 at 84h/85h) enables zero-overhead block transfers, and stretchable MOVX timing (2–9 cycles via CKCON.2–0) accommodates mixed-speed external peripherals without glue logic.

Key Specifications

Pinout & Package

DS87C520-QCL+ is housed in a 44-pin Plastic Leaded Chip Carrier (PLCC) package with J-lead configuration, rated for 0°C to +70°C operation and RoHS-compliant.

Key Features

Applications

Equivalent & Alternatives

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

Compared with DS83C520-QCL+, the DS87C520-QCL+ provides field-reprogrammable EPROM for iterative development, while AT89C51RD2-RLTUM trades architectural efficiency for higher Flash capacity but sacrifices deterministic timing control and integrated power management.

Availability

DS87C520-QCL+ is available at Aetrix Electronics and suitable for industrial automation, medical device manufacturing, smart metering, and legacy equipment retrofit requiring stable component supply and long-term lifecycle assurance.

Supply support for DS87C520-QCL+ 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 microcontrollers for demanding industrial and medical applications.

The DS87C520-QCL+ belongs to Maxim's high-speed 8051-compatible microcontroller family, engineered to deliver deterministic real-time performance, robust power management, and seamless legacy system upgrades without architectural compromise.

FAQ

What is the maximum operating frequency of the DS87C520-QCL+?

The DS87C520-QCL+ supports a maximum crystal frequency of 33MHz. At this rate, its 4-clock-per-machine-cycle architecture delivers a peak instruction execution speed of 8.25 million instructions per second (MIPS), with the fastest single-cycle instruction completing in 121ns. This is 2.5× faster than a standard 8051 running at the same crystal frequency, confirmed by the device's electrical specifications and timing diagrams in the official datasheet.

How does the ROMSIZE register in the DS87C520-QCL+ enable flexible boot memory management?

The ROMSIZE register (SFR address C2h) in the DS87C520-QCL+ allows software to dynamically configure the upper boundary of on-chip program memory-from 0kB to 16kB-in 1kB increments. This lets the DS87C520-QCL+ reserve lower memory pages (e.g., 0000h–0FFFh) as a secure boot block while mapping external Flash into the remaining 60kB address space, enabling safe firmware updates without hardware changes or external logic.

Can the DS87C520-QCL+ operate in low-power modes, and how is this controlled?

Yes, the DS87C520-QCL+ implements Power Management Mode (PMM) via the PMR register (C4h). Writing CD1/CD0 bits selects clock division by 64 or 1024, reducing the machine cycle rate to 187.5kHz or 11.7kHz at a 12MHz crystal. Hardware automatically exits PMM on interrupt or reset, and software can trigger exit via STOP bit clear. This feature is validated in the device's DC characteristics table and power consumption graphs.

What are the key differences between the DS87C520-QCL+ and DS83C520-QCL+?

The DS87C520-QCL+ contains 16kB of EPROM, allowing field reprogramming, while the DS83C520-QCL+ uses factory-masked ROM with fixed firmware. All other specifications-including speed, memory map, pinout, SFRs, and peripheral functionality-are identical. The DS87C520-QCL+ is intended for development and low-volume production; DS83C520-QCL+ targets high-volume cost-sensitive applications where firmware is finalized.

Does the DS87C520-QCL+ support dual serial communication, and how are the ports assigned?

Yes, the DS87C520-QCL+ integrates two independent full-duplex UARTs. UART0 uses P3.0 (RXD0) and P3.1 (TXD0) with standard 8051 SCON0/SBUF0 registers; UART1 uses P1.2 (RXD1) and P1.3 (TXD1) with dedicated SCON1/SBUF1 registers. Both support programmable baud rates, framing, and interrupt-driven operation, verified in the device's serial port functional description and register map.