Intel mcs-48 manual Adding 8 Input Lines

APPLICATION EXAMPLES

ADDING 8 INPUT LINES

+5V GND

C-l. L

		Vee	VOD Vss	Pl0	27
	2
				Pl1	28
- XTAL 1
				P12	29
-	3			P13	30
		XTAL 2		P14	31
				P15	32
	4			P16	33
				P17	34
- RESET
				P20	21
	7
				P21	22
- EA
			8049	P22	23
- ss			8048	P23	24
				P24	35
			8748				CLR
				P25	36			08
				P26	37			07
				P27	38			06
	1						74LS259	05
				DBO 12
_ TO						0	1161	04
39				081	13	A		03
_ Tl				D82 14				02
-	6			DB3 15			G	01
		iNT		DB4 16
				DB5 17
				DB6 18
				DB? 19

ADDING 8 OUTPUT LINES

The bus is normally used as an output port. To use it as an input port the bus is put in the high impedance state using the MOVX instruction and then read using the INS instruction. The resistor value chosen is a function of the output loading and the characteristics of the input signals.

Individual bits of the 74LS259 eight-bit addressable latch can be set or reset using the OUTL instruction. During the OUTL operation bit zero of the accumulator is written into the bit of the latch specified by bits 1 through 3 of the accumulator. In this configuration DSo- DS7 will be momentarily disturbed while the external latch is loaded.

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