NXP Semiconductors MC68020RC20E

Overview

MC68020RC20E from Motorola (later Freescale) is a 32-bit, second-generation enhanced microprocessor with full 32-bit data and address buses (A31–A0, D31–D0), on-chip 256-byte instruction cache, pipelined architecture, and support for coprocessor interface (CP0–CP3). It operates at 20 MHz, uses asynchronous bus timing, and targets embedded control and general-purpose computing systems requiring supervisor/user privilege separation and virtual memory support.

For engineers reviewing the MC68020RC20E datasheet, MC68020RC20E pinout, MC68020RC20E application, or MC68020RC20E equivalent, key selection criteria include its 20 MHz clock rating, 32-bit external bus width, on-chip instruction cache size, coprocessor interface protocol compliance, and RC-package thermal and mechanical specifications.

Technical Context

The MC68020RC20E implements a five-stage pipeline (fetch, decode, execute, memory access, write-back) with dynamic bus sizing and misaligned operand handling. Its bus interface supports asynchronous transfers using DSACK0/DSACK1 handshaking and includes dedicated function code (FC2–FC0), transfer size (SIZ1/SIZ0), and bus arbitration signals (BR, BG, BGA).

It features a 256-byte on-chip instruction cache organized as 64 lines × 4 bytes, controlled via the Cache Control Register (CACR), and supports cache reset and selective invalidation. Exception processing includes 256 vector locations, supervisor/user mode stack frames, and hardware-level bus error recovery using the Special Status Word (SSW).

Key Specifications

Pinout & Package

The MC68020RC20E is housed in a 132-pin ceramic leaded chip carrier (CLCC) package with side-brazed leads and integrated heat slug, rated for industrial temperature operation (–40°C to +85°C) and specified for 20 MHz operation under JEDEC JESD-22 conditions.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar 32-bit microprocessor applications.

Compared with MC68020RC20E, the MC68030RC25 adds integrated MMU and data cache for full virtual memory support, while the MC68EC020RC20 removes address bus width and MMU to reduce cost and power-both retain the same 20 MHz timing and CLCC packaging for drop-in replacement in non-MMU designs.

Availability

MC68020RC20E is available at Aetrix Electronics and suitable for industrial motion controllers, legacy workstation upgrades, communications protocol engines, and test equipment embedded controllers requiring stable component supply and long-term obsolescence management.

Supply support for MC68020RC20E 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

Motorola Semiconductor (later Freescale Semiconductor) was a pioneering U.S. semiconductor manufacturer known for the 68000 family, RF power transistors, and automotive ICs before its acquisition by NXP in 2015.

The MC68020RC20E belongs to the M68000 microprocessor family, designed for high-performance embedded and general-purpose computing systems requiring 32-bit processing, hardware privilege separation, and expandable coprocessor acceleration.

FAQ

What is the maximum operating frequency of the MC68020RC20E?

The MC68020RC20E is rated for a maximum clock frequency of 20 MHz, as confirmed by Motorola's Electrical Characteristics specification (Section 10.3) and Ordering Information (Section 11.1.1). This rating applies under industrial temperature conditions (–40°C to +85°C) with proper decoupling and signal integrity. Exceeding 20 MHz may result in undefined instruction execution or bus timing violations.

Does the MC68020RC20E include an integrated MMU?

No, the MC68020RC20E does not include an integrated Memory Management Unit. Unlike the later MC68030, it relies on external MMU chips (e.g., MC68851) for virtual memory support. The MC68020RC20E provides the necessary bus signals (FC, SIZ, AS, DTACK) and exception vectors required for external MMU interfacing, but all address translation and protection logic must be implemented externally.

What package type is used for the MC68020RC20E?

The MC68020RC20E uses a 132-pin ceramic leaded chip carrier (CLCC) package with side-brazed leads and an integrated copper heat slug. This package is designated "RC" in Motorola's ordering nomenclature and is mechanically and thermally specified in Section 11.2.1 of the M68020 User's Manual for industrial temperature operation.

How does the MC68020RC20E handle misaligned memory accesses?

The MC68020RC20E fully supports misaligned word and long-word accesses in hardware, automatically splitting them into multiple aligned transfers without software intervention. This behavior is documented in Section 5.2.2 and ensures correct execution of C-language structures containing packed or unaligned fields, unlike earlier 68k-family parts that generated address errors on such accesses.

Is the MC68020RC20E pin-compatible with the MC68EC020RC20?

The MC68020RC20E and MC68EC020RC20 share identical 132-pin CLCC packaging and pin assignments for all common signals (clock, data, control, power), but differ electrically on address pins A24–A31: these are no-connect on the MC68EC020RC20. Thus, they are mechanically pin-compatible but not functionally interchangeable without PCB redesign to accommodate the reduced address bus width.