Intel 8080 manual Applications Example, Iii, 1IIII~Iff1

APPLICATIONS EXAMPLE

The 8080 can be used as the basis for a wide variety of calculation and control systems. The system configura- tions for particular applications will differ in the nature of the peripheral devices used and in the amount and the type of memory required. The applications and solutions de- scribed in this section are presented primarily to show how microcomputers can be used to solve design problems. The 8080 should not be considered limited either in scope or performance to those applications listed here.

Consider an 8080 microcomputer used within an auto- matic computing scale for a supermarket. The basic machine has two input devices: the weighing unit and a keyboard, used for function selection and to enter the price per unit of weight. The only output device is a display showing the total price, although a ticket printer might be added as an optional output device.

The control unit must accept weight information from the weighing unit, function and data inputs from the key- board, and generate the display. The only arithmetic func- tion to be performed is a simple multiplication of weight times rate.

The control unit could probably be realized with standard TTL logic. State diagrams for the various portions could be drawn and a multiplier unit designed. The whole design could then be tied together, and eventually reduced to a selection of packages and a printed circuit board layout. In effect, when designing with a logic family such as TTL, the designs are "customized" by the choice of packages and the wiring of the logic.

If, however, an 8080 microcomputer is used to realize

the control unit (as shown in Figure 0-1),the only "custom" logic will be that of the interface circuits. These circuits are usually quite simple, providing electrical buffering for the input and output signals.

Instead of drawing state diagrams leading to logic, the system designer now prepares a flow chart, indicating which input signals must be read, what processing and computa- tions are needed, and what output signa Is must be produced. A program is written from the flow chart. The program is then assembled into bit patterns which are loaded into the program memory. Thus, this system is customized primarily by the contents of program memory.

For this automatic scale, the program would probably reside in read-only memory (ROM), since the microcom- puter would always execute the same program, the one which implements the scale functions. The processor would constantly monitor the keyboard and weighing unit, and up- date the display whenever necessary. The unit would require very little data memory; it would only be needed for rate storage, intermediate results, and for storing a copy of the display.

When the control portion of a product is implemented with a microcomputer chip set, functions can be changed and features added merely by altering the program in mem- ory. With a TTL based system, however, alterations may re- quire extensive rewiring, alteration of PC boards, etc.

The number of applications for microcomputers is limited only by the depth of the designer's imagination. We have listed a few potential applications in Table 0-2, along with the types of peripheral devices usually associated with each product.

	/	-	/	KEYBOARD				PRINTER
					00
				000	00	DISPLAY
				000				--- ..
		WEIGHING			00
				000	00	1':II':II':~I':ff':'1		CIJ
		UNIT		000	00
		1		1		T		+
								I
								I
							r ------ ,
		INPUT		INPUT		OUTPUT	I	OPTIONAL	I
							I	OUTPUT	I
		INTERFACE #1		INTERFACE #2		INTERFACE #1
								INTERFACE #2
							I		I
							' --- TT --
		+				ItI			J
CPU				1+				I L .. --
8080		I I						I tI
								I I

	BUS
CONTROL	It[	ItI
UNIT
	PROGRAM	DATA
	MEMORY	MEMORY
	(PROM)	(RAM)

Figure 0-1. Microcomputer Application - Automatic Scale

iii