Applications of the 8255A, Printer Interface

8255A18255A·5

APPLICATIONS OF THE 8255A

The 8255A is a very powerful tool for interfacing peripheral equipment to the microcomputer system. It represents the optimum use of available pins and is flex- ible enough to interface almost any 110 device without the need for additional external logic.

Each peripheral device in a microcomputer system usually has a "service routine" associated with it. The routine manages the software interface'between the device and the CPU. The functional definition of the 8255A is programmed by the 110 service routine and becomes an extension of the system software. By ex· amining the 110 devices interface characteristics for both data transfer and timing, and matching this infor· mation to the examples and tables in the detailed opera· tional description, a control word can easily be devel· oped to initialize the 8255A to exactly "fit" the applica- tion. Figures 17 through 23 present a few examples of typical applications of the 8255A.

INTERRUPT

REQUEST

PAc
PA,
PA,	HIGH-SPEED
	HIGH-SPEED
PA,	PRINTER

PA,

PAs

MODE 1	PA,
(OUTPUT)	PA,
(OUTPUT)
	PA,	HAMMER
		HAMMER
		RELAYS

PC,

--!C4

8255A

PB.

PB,

MODEl PB,

(OUTPUT)

PB,

PC,

PC,ACK

PC.

CONTROL LOGIC ANO DRIVERS

INTERAUPT

REQUEST

Figure 11. Printer Interface

INTERRUPT		I
REQU EST		I
		PC,	-	PAa	R.
		PC,

		8255A		PA,	R,
				PA,	R,	FULLY
				PA,	R,	DECODED
				PA,	R,	KEYBOARO
				PA,	R,	KEYBOARO
				PA,	R,
		MODE1		PAs	R,
		MODE1		PAs	SHIFT
		(INPUT)		PAs	SHIFT
		(INPUT)
				PA,	CONTROL
				PC,	STROBE
			-	PC,	ACK
			-
				-
				PB.	B.
				PB,	B,
				PB,	B,	BURROUGHS
				PB,	B,	SELF-SCAN
				PB,		SELF-SCAN
				PB,	B,	DISPLAY
				PB,	B,
				PB,	B,
		MODE 1 ---.j
	(OUTPUT)		,	PB,	BACKSPACE
			: PB7		CLEAR
			I PC,		DATA READY
			I PC,		ACK
				PC,	ACK
			i	PCs	BLANKING
		PC.		~C7	CANCEL WORD
INTERR UPT~
REQUEST

Figure 18. Keyboard and Display Interface

INTERRUPT		I
REOU EST		I
		pc,	PAc	R.
			PAc	R.
			PA,	-- R,
			PA,	R,
		MODE 1	PA,	R,	FULLY
			PA,	R,	DECODED
					DECODED
		(INPUT)	PA,	R,	KEYBOARD
			PA,	R,
			PAs	R,
		8255A	PA,	SHIFT
		8255A	PA,	CONTROL
			PA,	CONTROL
			PC,	STROBE
			PC,	ACKNOWLEDGE
			PC,	BUSY LT
			I PC,	TEST LT
			I PC,
	---- ,--				- -	"'0 - -
			PB.		- -	"'0 - -
			PB,		--	'1> - -
			PB,		--	'1> - -
		MODE 0	PB,		--	"'0 -	-
		(INPUT)	PB,		--	'1> - -
			PB,		--	0-	-
			PB,		--t> --		-
			lPB.		--0-.-		-
			PB,

TERMINAL

ADDRESS

Figure 19. Keyboard and Terminal Address Interface

9-31	AFN-00744A-15

Intel mcs-48 manual Applications of the 8255A, Printer Interface

Models: mcs-48