How to Interface 8251 with 8086

Interfacing 8251 with 8086

Tags: Uart assembly program for 8086,serial communication using 8086,rs232 communication using 8086, Assembly program to interface 8251 with 8086, Circuit Diagram to Interface 8251 with 8051,
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8251-ps2-lab-kit-8086
8086 Trainer Board

The 8086 trainer kit is specifically designed to help students to master the required skills in the area of embedded systems. The kit is designed in such way that all the possible features of the microprocessor will be easily used by the students. MICROPROCESSOR offers more advantages than conventional discrete hardwired logic circuits. The major advantage is its programmability to adapt to different environment and in addition it reduces the PCB space.


8251 (USART)

The RS232C interface of PS-TIMER & USART comprises of the universal synchronous/asynchronous receiver/transmitter 8251 (USART), RS232C driver max 232.


The 8251A is used here as a peripheral device for serial communication and is programmed by the CPU to operate using virtually any serial data transmission technique. The USART accepts data characters from the CPU in parallel format and then converts them into a continuous serial data stream for transmission. Simultaneously, it can receive serial data streams and convert them into parallel data characters for the CPU. The CPU can read the status of the USART at any time. These include data transmission errors and control signals.


Interfacing 8251 with 8085

Microprocessor don’t have the direct serial communications, so to communicate the data serially to a device we need a driver to send a character serially, here we use 8251. 8251 is a driver which converts the parallel data to a serial data the pin detail and control pins are given so according to that we can develop the hardware.


Obviously, 8251 is not directly compatible with these signal levels. Standard method to interface RS232C and TTL levels is with MC1488 quad TTL-to-RS232C drivers and MC1489 quad RS232C-to-TTL receivers. Of the 25 handshake signals provided by the RS232C standard, we will discuss only four signals which are used in our design. They are the RTS, CTS, RxD and TxD signals.


Pin Assignment with 8086

 


 

8086

8251

8251 PIN DIAGRAM

CONTROL L LINES

13

A1

                 8255-pin-diagram-for-8086

29

RD

30

WR

24

CLK

3

RST

From decoder

CS

8251 – DATA LINES

12

D0

13

D1

14

D2

15

D3

16

D4

17

D5

18

D6

19

D7

VCC

40

26

Address line and data lines are Decoded using Latch

GND

20

7


 

Circuit Diagram to Interface 8251 with 8086



circuit-diagram-to-interface-8251-with-8051



Assembly program to interface 8251 with 8086

***************************************************************************************


Title : To transmit a character from 8251 to the HyperTerminal using 8086


***************************************************************************************

 


MEMORY

OPCODE

MNEMONICS

1100

Be 00 15

MOV SI,1500H

1103

B0 36

MOV AL,36H

1105

BA 06 FF

MOV DX,FF06

1108

EE

OUT DX,AL

1109

B0 40

MOV AL,40H

110B

BA 04 FF

MOV DX,FF04

110E

EE

OUT DX,AL

110F

B0 01

MOV AL,01H

1111

BA 04 FF

MOV DX,FF04

1114

EE

OUT DX,AL

1115

B1 05

RELOAD: MOV CL,05H

 1117

BA 12 FF

CHECK: MOV DX,FF12

111A

EC

                IN AL,DX

111B

24 02

AND AL,02H

111D

74 F8

JZ CHECK

111F

BA 10 FF

MOV DX,FF10

1122

EC

IN AL,DX

1123

88 04

MOV [SI],AL

1125

46

              INC SI

1126

3C 3F

CMP AL,3FH

1128

75 EB

JNZ RELOAD

112A

FE C9

DEC CL

112C

75 E9

JNZ CHECK

112E

CD 02

INT 02

1130

CD 02

INT 02


 
 
ADDRESS     DATA

1500     48H,45H,4CH,4CH


1504     4FH,2DH,38H,30H (HELLO-8086)


1508     38H,35H,0AH,0DH


150C     END

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