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Chapter 35 ½ P1C1650: Chip Architecture and Operation 603

GI initiated a design effort that generated the "A" series of PIC chips-PIC 1650A, PIC 1655A-that are identical to the original except that the operating voltage range was in creased from 4.75-5.25 V to 4.5-7 V. As four C cell batteries fully charged produce 6.8 V in series, 7 V was chosen as the upper limit.

Several versions of the PIC 1650 have been architectured which, among other things, vary according to number of I/O lines, RAM size, and ROM size. These are enumerated in Table 1.

Applications using the PIC series have centered around those where a single-chip microcomputer could perform systems functions at a lower cost than non-computer solutions presently available or, alternatively, provide extra features which heretofore would have been prohibitively expensive without a microcomputer. Present applications that use the PIC chip include:

Digital-readout weight scale. In this application, weight is converted to a digital pulse train via a front-end transducer circuit. The pulses are applied to the RTCC (Real Time Clock Counter) input. The ROM program computes the difference between the frequency with the weight applied and the no-weight frequency (thereby providing for auto-zero correction) and converts the difference to a 4-digit BCD number which is subsequently displayed. To save multiplexing costs, all thirty-two I/O lines drive the display directly.

Auto-dialer telephone system. This system is capable of storing and retrieving sixteen 10-digit telephone numbers. Here, the PIC chip processes command codes, which are entered through the keyboard, and drives outboard CMOS RAM, which stores the actual digits.

Motor control. In this application, the PIC chip serves as a feedback element in a constant-speed motor control system. The microcomputer senses the present speed of the motor and adjusts the firing pulse to an external SCR, which, in turn, drives the motor. The high instruction rate permits precise control over a wide range of speeds. Typical applications of this system are found in industrial drill presses and hand drills.

Consumer electronics. In the consumer arena, the PIC has been programmed into a variety of electronic games. The PIC is quite efficient in the area of sound generation: the high instruction rate permits higher-frequency sounds and thus more complex sounds than would be possible with a slower processor. Other areas of consumer electronics use the aforementioned motor control technique in household mixers, blenders, and food processors. The PIC has also been designed into appliances requiring time controlling, such as microwave oven timing.

Figure 1 shows a functional block diagram of the PIC 1650. All data elements-arithmetic logic unit, register file array, I/O registers-are connected via an internal 8-bit bidirectional bus.

Table 1 Family of PIC Architectures

	PIC1650A	PIC1655A	PIC1670	PIC1645	PIC1656
Technology	NMOS	NMOS	NMOS	NMOS	NMOS
Number of pins per package	40	28	40	18	28
Cycle time (m sec)	4	4	4	4	4
Data path width (bits)	8	8	8	8	8
Instruction word width (bits)	12	12	12	12	12
Program ROM size (12-bit bytes)	512	512	1024	256	512
Number of fixed instructions	30	30	33	31	31
Data storage RAM size (8-bit bytes)	32	32	64	24	32
Operating-voltage supply range (volts)	4.5-7.0	4.5-7.0	4.5-7.0	4.5-7.0	4.5-7.0
Interrupt capability	No	No	Yes	Yes	Yes
Levels of pushdown stack	2	2	4	3	3
I/O configuration (registers) Input/output Input only Output only	4 8-bit	1 8-bit 1 4-bit 1 8-bit	4 8-bit	1 4-bit 1 4-bit 1 4-bit	1 8-bit 1 4-bit 1 8-bit
Date of introduction 1979	1978	1978	Planned 1979	Planned 1979

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