Stack Computers: the new wave © Copyright 1989, Philip Koopman, All Rights Reserved.

Chapter 4
Architecture of 16-bit Systems

In this chapter we shall discuss a representative selection of 16-bit stack computer designs. The designs have been chosen to span a wide range of implementation philosophies and tradeoffs. Section 4.1 discusses the characteristics of 16-bit systems. An important consideration is that 16-bit hardware is compact enough to allow for complete systems on a single chip for embedded control applications.

The remaining sections discuss four different 16-bit stack computers. The sections are arranged in order of increasing integration level, from a system made with off-the-shelf discrete components to a highly integrated processor-on-a-chip.

In Section 4.2 we discuss the WISC CPU/16, a discrete component implementation of a generalized stack processor with a writable control store. The CPU/16 is a technology development platform designed for simplicity and flexibility.

In Section 4.3 we discuss the MISC M17 processor. The M17 is targeted at "low end," price-sensitive applications. Consequently, it keeps its stacks in program memory to eliminate the cost of separate stack memory hardware.

In Section 4.4 we discuss the Novix NC4016, which was the first Forth chip to enter the marketplace. The NC4016 provides an intermediate range of price and performance, with dedicated off-chip stack memories.

In Section 4.5, we discuss the Harris RTX 2000, which is a high performance microcontroller based on the Novix NC4016 design. The RTX 2000 uses a standard cell design approach, which enables it to include on-chip stack memory for speed and compactness. The standard cell approach also allows the addition of a hardware multiplier and counter/timers to the processor chip.

The CPU/16, NC4016, and RTX 2000 are ML0 stack machines. The M17, in keeping with its emphasis on low cost, as an MS0 stack machine.

• 4.1 CHARACTERISTICS OF 16-BIT DESIGNS
  • 4.1.1 Good fit with the traditional Forth model
  • 4.1.2 Smallest interesting width
  • 4.1.3 Small size allows integrated embedded system
• 4.2 ARCHITECTURE OF THE WISC CPU/16
  • 4.2.2 Block diagram
  • 4.2.3 Instruction set summary
  • 4.2.4 Architectural features
  • 4.2.5 Implementation and featured application areas
• 4.3 ARCHITECTURE OF THE MISC M17
  • 4.3.2 Block diagram
  • 4.3.3 Instruction set summary
  • 4.3.4 Architectural features
  • 4.3.5 Implementation and featured application areas
• 4.4 ARCHITECTURE OF THE NOVIX NC4016
  • 4.4.1 Introduction
  • 4.4.2 Block diagram
  • 4.4.3 Instruction set summary
  • 4.4.4 Architectural features
  • 4.4.5 Implementation and featured application areas
• 4.5 ARCHITECTURE OF THE HARRIS RTX 2000
  • 4.5.1 Introduction
  • 4.5.2 Block diagram
  • 4.5.3 Instruction set summary
  • 4.5.4 Architectural features
  • 4.5.5 Implementation and featured application areas
  • 4.5.6 Standard cell designs

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Phil Koopman -- koopman@cmu.edu