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584 Part3½ Computer Classes Section 1½ Monolithic Microcomputers

architecture with the largest installed base. The internal clock rate varies from 200 to 450 KHz, depending on technology.

A follow-on to the TMS1000 is the TMS7000 series announced in 1981 [Hayn, McDonogh, and Bellay, 1981]. The TMS7000 is an 8-bit monolithic microcomputer with 2 or 4 Kbyte a user-definable instruction set. The first two chips, the 7020 and 7040, have 2 or 4 Kbyte of use ROM respectively, and 128 bytes of RAM in a 40-pin package. Up to 60 Kbyte of external memory can be added. A complete family of monolithic microcomputers is planned.


In 1978, General Instrument Corporation (GI) introduced a single-chip computer called the PIC 1650 (Programmable Intelligent Controller). Five variations have been produced varying in number of pins (18 to 40), amount of ROM (256 to 1,024 twelve-bit words), amount of RAM (24 to 64 eight-bit bytes), and operational voltage range. The large majority (67 to 80 percent) of the pins are devoted to program-controlled I/O.

GI sought an easy-to-program, general-purpose microcontroller. Thus the PIC1650 differs from the TMS1000 in several significant areas:

Adherence to the single-word instruction format (which simplifies the implementation of the 1650) poses serious problems for expansion when technology allows more ROM to be implemented on a chip and control applications require more than the 256 to 1,024 words of program in the current PIC architecture. The small-address-space problem has been encountered in all classes of computers; hence there is a wide range of solutions that have historically been tried. The following is a list ordered from smallest to greatest impact on existing user code: The PIC 1650 has been used in electronic toys (by Ideal Toy and Coleco), electronic scales (Detecto), and cameras (Bosch).

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