Intel 8080 manual Format

The three 8212s can be used to drive long lines or LED indicators due to their high drive capability. (15mA)

O-DATA

C/DCONTROL 1-COMMAND

_____________________ 8251SELECT

(ACTIVE LOW)

Figure 3-13. 8251 Format.

The two (2) 8255s provide twenty four bits each of programmable I/O da~a and control so that keyboards, sen- sors, paper tape, etc., can be interfaced to the system.

________________________ 8212 #1 SE LECT

(ACTIVE HIGH)

___________ 8212 #2 SELECT

(ACTIVE HIGH)

_____________ 8212 #3 SELECT

(ACTIVE HIGH)

Figure 3-15. 8212 Format.

OO-PORTA 01-PORTB 10 -PORTC

11-COMMAND

}	PORT SELECT
'---	8255 #1 SELECT
	(ACTIVE LOW)

"-------8(~g::~~i~E~;r

Figure 3..14. 8255 Format.

SERIAL DATA

COMMUNICATION

8251

Addressing the structure is described in the formats il- lustrated in Figures 3-13, 3-14, 3-15. Linear Select is used so that no decoders are requ ired thus, each device has an ex- clusive "enable bit".

The example shows how a powerful yet flexible I/O structure can be created using a minimum component count with devices that are all members of the 8080 Microcomputer System.

#2	#1
8255	8255

D~.Do cs Ao A,

DATA BUS

CONTROL BUS

8212	8212		8212
#3	#2		#1
	MD	MD	MD

Figure 3-16. Typical I/O Interface.

3-10