8251

PROGRAMMABLE COMMUNICATION INTERFACE – IC 8251

AIM:

            To establish the communication between two microprocessor systems using

RS 232C.

APPARATUS REQUIRED:

            1. RS 232 Cable

            2. 8251 – Interface board

            3. 8085 – Microprocessor kit (2)

            4. Flat ribbon cable

DESCRIPTION:

            IC 8251 – PROGRAMMABLE COMMUNICATION INTERFACE

The 8251 is used here as a peripheral device for several communication and is programmed by CPU to operate using virtually any several data transmission technique.

The USART accepts data characters from the CPU in parallel Format and converts to several and it also receivers several data and convert to parallel.

            Main Features of 8251 are

                     1) Both Synchronous and Asynchronous operation

                     2) False start bit detection

                     3) Automatic break detect and handling

                     4) Clock rate 1, 16, or 64 time band rate

                     4) Error detection - parity, overrun and framing errors.

                     5) Break characters generation

  The control pins with which the 8251 A communicates with the CPU are the RESET,

CLK WR, RD, CS, D0-D7

CONTROL SIGNAL 8251A:

                     Obviously a USART such as the 8251 A is not directory compatible with RS 232C signal levels we can interface TTL signals of the 8251A to RS 232C signals If the Jumper in this interface and removed and the jumpers in the jumper table under CRT are inserted then this circuit will produce and accept RS232C signals. The 8251A is used as the serial port on SDIC-86 boards.  It is also used on the IBM PC synchronous communication board and on many other boards.  The D0-D7 act as data bus the chip select is input is connected to an address decoder so the device is enabled when addressed. C/D means control or data is to be write read RD read data command WR write data or Control command .The TXC is the transmit shift register clock input RXC is the receive shift register input when connected with another system for several communication the signals With connect with CTS, RTS, TXD and RXD signals of that system

CTS: Clear to send: Enable 8251 to transmit several data

RTS: Request to send: When low, indicates that 8251 A can receive serial data

TXD: Transmit serial data

RXD: Receive serial data.

ALGORITHM:

            1. Start the program

             2. Initialize the mode format of 8253

            3. Get the i/p to check for transmitter empty

            4. And immediately 04 with the accumulator

            5. Jump on zero to step 3

            6. Transmit the data

            7. Stop the program

MASTER PROGRAM: TRANSMITTER PROGRAM

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4100	3E,36	START	MVI A, 36	MODE SET FROM 8253
4102	D3,CE		OUT 0CEH
4104	3E,0A		MVI A, 0A	TIMER INITIALIZATION
4106	D3,C8		OUT DC8H
4108	3E,00		MVI A, 00
410A	D3,C8		OUT OC8H
410C	3E,4E		MVI A,4E	MODE SET FOR 8251
410E	D3,C2		OUT 0C2H
4110	3E,37		MVI A,37
4112	D3,C2		OUT 0C2H
4114	DB,C2	LOOP	IN 0C2H	CHECK FOR TRANSMITTER EMPTY
4116	E6,04		ANI 04
4118	CA,14,41		JZ LOOP
411B	3E,41		MVI A,41H
411D	D3,C0		OUT 0COH	DATA IS TRANSMITTED.
411F	CF		RST 1

SLAVE PROGRAM: RECEIVER PROGRAM

ADDRESS	OPCODE	LABEL	MNEMONICS	COMMENTS
4200	3E,36	START	MVI A, 36	MODE SET FOR 8253
4202	D3,CE		OUT 0CEH
4204	3E,0A		MVI A, 0A
4206	D3,C8		OUT  OC8H
4208	3E,00		MVI A, 00
420A	D3,C8		OUT 0C8H
420C	3E,4E		MVI A,4E	MODE FOR 8251
420E	DE,C2		OUT 0C2H
4210	3E,37		MVI A, 37	STATUS WORD FOR 8251.
4212	D3,C2		OUT 0C2H
4214	DB,C2	LOOP1	IN 0C2H	CHECK RECIVER IS READY
4216	E6,02		ANI 02
4219	CA,14,42		JZ LOOP1	JUMP ON ZERO TO ADDRESS
421B	DB,C0		IN 0C0H
421D	32,50,41		STA 4150H	STORE DATA
4220	CF		RST 1

OUTPUT:

Master:         TRANSMITTER END - 41           Slaves:           RECEIVER END - 41

RESULT:

            Thus the interface program for communication between two microprocessor using RS 232C was executed and the results are verified.