Aim: Write a Program to read 16 bit Data from a port and display the same in another port.

Objectives: [

• To learn configuring of Key board and display module with 8086 microprocessor using 8255PPI
• Design algorithm and develop a program for accepting data from oneport and displaying it to LCD connected to other port.

Equipment Require:

8255 Display Module, 8086 trainer Kit

Theory: A Simple approach

We can make use of the 8086 IN and OUT instruction to read the data from the device attached to a port and send the data to another port.

We can access the ports using direct addressing or indirect addressing

Direct address can be provided in the instruction

Indirect address is loaded in DX register.

here is  simple program statements for the reading from a port and writing to another port.

MOV DX, 0125h   ; Load DX with the input port address

IN AL, DX             ; Read the data in register AL from the specified port

MOV DX, 0135h  ; Load the output port address in DX register

OUT DX, AL        ; Transfer the data in AL at the specified port

HLT

Program to display data on various ports Using Kit

Figure below shows the arrangement of the 8-LED on PA, PB, PC and the data lines. When the users write certain binary data on these ports, the LED whose bit is high will glow. Thus for example if we pass AA on portA the its equivalent binary 10101010 so the LEDs corresponding to high (‘1’) will glow.

Procedure

1. Connect the card to the 50-pin FRC cable. Ensure pin-1 of the card is connected to pin-1 of the kit bus connector
2. Select SW-2 on card to OFF position and Enter the program given next in the kit memory using ‘S’ (SUB_MIR) command
3. Execute the program by ‘GO’ command. Observe the display on the LEDs corresponding to the data sent on a port and also on the data lines LEDs
4. Press SW1 on the card and observe the LEDs status as per the program given next.

Command word for 8255

D7	D6	D5	D4	D3	D2	D1	D0	CW	Description
1	0	0	0	0	0	0	0	80h	All ports as o/p

Port Addresses

D7	D6	D5	D4	D3	D2	D1	D0	Port Address	PORT
1	0	0	0	0	0	0	0	80h	PA
1	0	0	0	0	0	1	0	82h	PB
1	0	0	0	0	1	0	0	84h	PC
1	0	0	0	0	1	1	0	88h	CWR

Program to display the LEDs on various ports interfaced on 8255 ports

Here we configure the control word register in I/O mode with all ports as simple outputs

Address	OPCODE	LABEL	MNEMONICS	Comment	Description
1000:0100	BO 80	STSRT:	MOV AL, 80	Configure PA,PB,PC as o/p
: 0102	BA 86 00		MOV DX, 86
:0105	EE		OUT DX, AL		OBSERVE 80(10000000) ON DATA LINE ledS
:0106	B0 AA	LOOP:	MOV AL, AAh
:0108	BA 80 00		MOV DX, 80h
:010B	EE		OUT DX, AL		Observe Port-A LEDs
:010C	BA 82 00		MOV DX, 82h
:010F	EE		OUT DX, AL		Observe Port-B LEDs
:0110	BA 84 00		MOV DX, 84h
:0113	EE		OUT DX, AL		Observe Port-C LEDs
:0114	B9 FF FF		MOV CX, FFFFh
:0117	CD AA		INT AA	CALL DELAY Sub Routine
:0119	B0 55		MOV AL, 55h
:011B	BA 80 00		MOV DX, 80h
:011E	EE		OUT DX, AL		Observe Port-A LEDs
:011F	BA 82 00		MOV DX, 82h
:0122	EE		OUT DX, AL		Observe Port-B LEDs
:0123	BA 84 00		MOV DX, 84h
:0126	EE		OUT DX, AL		Observe Port-C LEDs
:0127	B9 FF FF		MOV CX, FFFFh
:012A	CD AA		INT AA	Call Delay
:012C	EB D8		JMP 0106	LOOP Back

Outputs:

Observe the outputs on PA, PB, PC

Press SW1 and again observe the LED display on various ports.

ViVa Questions:

Que-1 : Write the control word format for configuring all ports in simple i/o mode

Ans:

D7	D6	D5	D4	D3	D2	D1	D0	CW	Description
1	0	0	0	0	0	0	0	80h	All ports as o/p
i/o mode	Gp A in mode-0		PA as o/p	PCUpper as o/p	Gp as mode-0	PB as o/p	PCLower as o/p

Que 2: What is the purpose of INT AA ?

Ans: This is an software interrupt call. interrupt number is AA. this interrupt causes the call to delay subroutine.

Que 3: What are the port address used in this program for various ports of 8255?

Ans:

PA address  = 80h

PB address  = 80h

PC address  = 80h

CW Register address  = 80h