Intel mcs-48 manual Applications, General Block Diagram

8279, 8279-5

Entry appears to be from the initial entry point.

8/16 Character Display Formats

If the display mode is set to an 8 character display, the on duty-cycle is double what it would be for a 16 character display (e.g., 5.1 ms scan time for 8 characters vs. 10.3 ms for 16 characters with 100 kHz internal frequency).

G. FIFO Status

FIFO status is used in the Keyboard and Strobed Input modes to indicate the number of characters in the FIFO and to indicate whether an error has occurred. There are two types of errors possible: overrun and underrun. Overrun occurs when the entry of another character into a full FIFO is attempted. Underrun occurs when the CPU tries to read an empty FIFO.

The FIFO status word also has a bit to indicate that the Display RAM was unavailable because a Clear Display or Clear All command had not completed its clearing operation.

In a Sensor Matrix mode, a bit is set in the FIFO status word to indicate that at least one sensor closure indication is contained in the Sensor RAM.

In Special Error Mode the S/E bit is showing the error flag and serves as an indication to whether a simultaneous multiple closure error has occurred.

FIFO STATUS WORD

,FIFO Full

Flag for

APPLICATIONS

							SHIFT		KEVBOARD
									MATRIX
						CONTROL
							8/	8 COLUMNS
							RETURN		8 ROWS
							LINES
									'>-
							3			8
		INT	SHIFT CNTL			"0voo_7
			INT					3-8 DECODER
8-81T		DATA BUS				v..	Jv		~
	DATA
SYSTEM
MICRO-		~	DO_7
PROCESSOR	BUS									3lsa
		iijj	lOR			80 _3	4/
		WR		8279			SCAN LINES		(:'
CONTROLS {			lOW
		RESET
		CS	RESET
ADDRESS {			CS					4--16 DECODER
		c/o							r;6
	BUS		c/o
		ClK
	CLOCK		CLK SO	_3	A O_ 3 BD
							BLANK
					I	~'~lAY
						4			ADDRESSES
									(DECODED)

	DISPLAY
4	CHARACTERS
	DATA
/
	DISPLAY

FIGURE 2. GENERAL BLOCK DIAGRAM

9-77 AFN-00742A-08