For an LSI machine to perform higher-level operations with ease, microinstruction sequences corresponding to common higher-level functions are stored in a separate read-only memory (ROM) to be accessed, decoded, and executed on command. These high-level sequences are called macroinstructions, the medium in which system programmers usually code. Macroinstructions in a microcomputer correspond to the basic instructions of a minicomputer. Microprogramming enables a systems designer to adapt standard hardware to specific applications - perhaps the most useful characteristic of a microcomputer, The designer can construct macroinstructions that are best suited for the particular functions to be performed, and incorporate them into the microprocessor. For example, the instruction set of an existing minicomputer can be completely or partially emulated to minimize software development. Alternatively, a machine can be built to perform functions peculiar to an application such as word processing or data acquisition. This capability to adapt a standard set of hardware modules to a variety of problems combines the cost advantages of high-volume chip production with the computing efficiency of tailored instruction sets. MICROCOMPUTER vs MINICOMPUTER Although stark and simplistic price comparisons are sometimes misleading, it is not unfair to say that an LSI microprocessor has a substantial cost advantage over a typical minicomputer CPU. For example, a complete LSI CPU may be purchased for as little as $300, compared to $1000 to $2000 for a minicomputer CPU. The CPU power consumption of an LSI microcomputer is 66 to 75 percent less than that of a comparable minicomputer. For a system containing but one CPU, the difference would not be significant considering the overall system's power requirements. However, in applications where many CPUs are required, the power difference would he substantial. An MOS/LSI microcomputer operates at 50 to 33 percent of the speed of commercially available minicomputers. Typical memory-to-memory add times for a moderately priced mini are An example of a microcomputer is Teledyne Systems' TDY-52, a programmable microcomputer contained within a 2" x 2" x O.2" package. Teledyne offers two different configurations of the TDY-52: the TDY-52A, a package holding a CPU with 8 registers, a 4K x 8-bit microinstruction ROM control memory, 4K x 8-bit application program RAM memory, a 2K bit scratchpad RAM, input multiplexer, between 5 and Z0 microsec compared to 15 to 60 microsec for a microcomputer. The speed of a microcomputer is derived from the particular MOS process used in fabrication. As these processes improve, so will the speed. With integrated circuits, system reliability is largely a function of the number of printed circuit (PC) board interconnections. Since each LSI package replaces from 50 to 100 TTL packages. the interconnections required by microcomputers are reduced and total system reliability is increased. The LSI microcomputer can be built into a light and compact configuration because of the higher number of gates per package module and the simplicity of interconnection. In summary, the LSI microcomputer offers better price-performance, lower power consumption and heat dissipation, higher reliability, and smaller physical size than a minicomputer. The microcomputer further offers the flexibility of microprogramming, which, in a given application, has many advantages. Although execution speeds comparable to today's minicomputer have not yet been achieved, several architectural techniques have emerged which will eventually increase microcomputer speeds. CHARACTERISTICS Microprocessor architecture is similar to that of a bus-oriented minicomputer. Applications can generally be categorized by bit width: four-bit microprocessors for calculators; eight-bit units for microcontrollers; and sixteen-bit units for microcomputers. The range of characteristics is broad: Data Word Size 4 to 100 bits Instruction Set 40 to 120 Instruction Format 8 to 24 bits ROM 400 23-bit to 16K 8-bit RAM up to 65K 16-bit General-Purpose Registers 1 to 16 Cycle Time to Fetch & Execute An Instruction 0.54 to 62 microsec, with 5 to 10 microsec common Stack Depth 2 to 32 levels Interrupt Cepebility None to full Parallelism mostly parallel to serial/parallel output buffer registers, priority interrupts, and oscillator; and the TDY-52B, a general-purpose 16-bit microcomputer with CPU and registers, priority interrupt, memory and I/O address register, clock generator, timing and control, and output buffers. Both configurations can also incorporate additional ROM, RAM and ROM/RAM modules, contained within another TDY-52 size package.