Intel mcs-48 manual Ii Aa, Read OO-Port #4 Write Port #5 10 or Port #6 Port #7

EXPANDED MCS-48 SYSTEM

another using standar.d MCS-80/85 I/O devices; and a third "using the combination memory/I/O expander devices the 8155, 8355, and 8755. It is also possible to expand using standard TTL devices as shown in Chapter 5.

3.3.1 I/O Expander Device

The most efficient means of I/O expansion for small systems is the 8243 I/O Expander De- vice which requires only 4 port lines (lower half of Port 2) for communication with the 8048. The 8243 contains four 4-bit I/O ports which serve as extension of·the on chip I/O and are addressed as ports #4-7. The follow- ing operations may be performed on these ports:

1.Transfer Accumulator to Port.

2.Transfer Port to Accumulator.

3.AND Accumulator to Port.

4.OR Accumulator to Port.

A4-bit transfer from a port to the lower half of the Accumulator sets the most significant four

bits to zero. All communication between the 8048 and the 8243 occurs over Port 2 lower

(P20-P23) withtimiilg provided by an output pulse on the PROG. pin of the processor~ Each

transfer consists of two 4-bit nibbles:

The first containing the "op code" and port address and the second containing the actual 4 bits of data.

Nibble 1Nibble 2

3	2	1	0	3	2	1	0
	II	I A I A I		Id Id Id Id I

Instruction Port data

Code Address

IIAA

00 Read	OO-Port #4
01 Write	01-Port #5
10 OR	10-Port #6
11 AND	11-Port #7

		EXPANDER INTERFACE
			fl CHIP SELECT CONNECTION IF MORE
			-=-	THAN ONE EXPANDER IS USED
	A-	~	CS			..
	(' 20	I/O
	PROG "	...>		P4	4	I/O
			PROG		"	v
	A	] TEST		P5	4	I/O
	2
8048		INPUTS	8243			v
	"					..
					4
	A			P6		I/O
						v
P20-P23		4	DATA IN
	"	v	P2	P7	4	" I/O
						v

OUTPUT EXPANDER TIMING

PROG	\___-----..11		BITSD.l		BITS 2.3
	~___~X_____~)~·~-	DO}01	PORT	DO} READ
				01	WRITE
		10	ADDRESS	10	OR
		11		11	AND

P20·P23

ADDRESS (4-BITS) DATA (4-BITS)

ANDOPCODE

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