Peripheral - 8255

PROGRAMMABLE PERIPHERAL INTERRUPT PERIPHERAL INPUTS AND OUTPUT – 8255

AIM:

            To study the mode 0 and mode 1 Characteristics of 8255 PPI in 8085 MP system using SPDT switches & LED’s

APPARATUS REQUIRED:

1. 8255 – Peripheral input and output board

            2. 8085 – Microprocessor kit

            3. Flat ribbon cable.

MODE 0:

AIM:

            To Initialize the port A as input port and port as output Port in mode 0, to input the data at port A as set by the spit switches and to output the same data as Port B to glow the LED’s

ALGORITHM:

            1. Enter the program starting from the user RAM address 4100

            2. Set a known data at the SPDT switches

            3. Execute the program

            4. Initialize port A as an input port

1.      The data as set by the accumulator and is stored in 4500

2.      Please verify whether the data at 4500 is the same as that of set by SPDT switches.

PROGRAM

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4100	3E		MVI A, 90	IINITIALIZE PORT A AS SPDT
4101	90
4102	D3		OUT 0C6H	OUT THE CONTROL PORT
4103	C6
4104	DB		IN OCOH	READ PORT A
4105	CO
4106	D3		OUT OC2H	STORE IT AT 4500
4107	C2
4108	76		HLT	STOP THE PROGRAM

MODE 1

AIM

            To initialize Port A as input port and port B as output port in mode 0,to input the data at Port A as the set by the SPDT switches and to output the same data as port B to glow the LED’s accordingly

ALGORITHM:

            1. Enter the program starting from the user RAM address 4100

            2. Set a known data at the SPDT switches and executes the program

            3. Initialize port A as input port and port B as output port

4.The data as set by SPDT switches setting is input to the accumulator and is outputted to port B           

5.Please verify visually that the data output at the LED’s is the same as that set by the SPDT switch setting S.

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4100	3E		MVI A, 90	MOVE THE DATA 90 TO A REG
4101	90
4102	D3		OUT 0C6H	OUT TO CONTROL PORT
4103	C6
4104	DB		IN 0C0DH	READ PORT
4105	C0
4106	D3		OUT 0C2H	OUT TO CONTROL PORT
4107	C2
4108	76		HLT	STOP THE PROGRAM

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4200	DB, 00	INT	IN 000H	READ PORT A
4202	32,00,45		STA 4500	STORE THE RESULT
4205	76		HLT	STOP THE PROGRAM

MODE TWO

             To initialize port A as an input port in Mode 1 to enable RST 5.5 interrupt of 8085 CPU and to input the data to the CPU in configuration with the hand shaking signals

ALGORITHM:

            1. Enter the main program starting from the user Ram address 4100

2. Enter the ISR starting from user RAM address 4200

            3. Enter the jump 4200 op code from location 4010

            4. Execute the main program set a known data at the SPDT switches.

            5. Input the data by pressing INTI switch

6. The 8255 i/p the data at port A stores the data in its buffer and then interrupts the CPU

            7. The ISR i/p the data from 8255 i/p buffer and stores it location 4500

PROGRAM:

ADDRESS	OPCEDE	LABEL	MNEMONICS	COMMENTS
4100	3E,B6		MVI A, B6	PORT A AS AN I/P
4102	D3, C6		OUT 0C6H	PORT IN MODE1
4104	3E, 09		MVI A, 09	SET THE PC4 BIT
4106	F3			ENABLE INTERRUPT
4107	3E, 08		MVI A, 08	ENABLE RST 5.5
4109	30
410A	FB		E1
410B	76		HLT	STOP THE PROGRAM

           

ISR 1 INTERRUPT SERVICE ROUTING

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4200	DB, 00	INT	IN 000H	READ PORT A
4202	32,00,45		STA 4500	STORE THE RESULT
4205	76		HLT	STOP THE PROGRAM

RESULT:

            Thus the AL program was written to perform the generation square wave using 8255 and executed successfully.