We interface the I/O device in a very segmented manner and is carried systematically. In the interfacing of seven segment display to 8085 microcontroller it is found that An output device which is very common is, especially in the kit of 8085 microprocessor and it is the Light Emitting Diode consisting of seven segments. Moreover, we have eight segments in a LED display consisting of 7 segments which includes ‘.’, consisting of character 8 and having a decimal point just next to it. We denote the segments as ‘a, b, c, d, e, f, g, and dp’ where dp signifies ... Read More

We write an 8085 assembly language program for the addition of 4 hex digits of a 16-bit number whose input is given from the keyboard and the result is displayed in the data field.FILE NAME ADDHEX.ASM ORG C000H CURDT: EQU FFF9H UPDDT: EQU 06D3H GTHEX: EQU 052FH HXDSP: EQU 05A1H OBUFF: EQU FFFAH MVI A, 0EH SIM EI ; Unmask RST5.5 and enable interrupts MVI B, 00 CALL GTHEX ; Input a 4 digit number and display in address field CALL HXDSP ; Store the 4 hex digits in 4 locations starting from OBUFF LXI H, OBUUF MOV A, M ... Read More

We write an 8085 assembly language program of two input using two 2-digit hexadecimal numbers from the keyboard and then we add and the output results in the address field.FILE NAME ADD2NUM.ASM ORG C000H CURAD: EQU FFF7H UPDAD: EQU 06BCH CLEAR: EQU 044AH GTHEX: EQU 052FH MVI A, 0EH SIM EI ; Unmask RST5.5 and enable interrupts MVI B, 01 CALL GTHEX ; Input a 2 digit number and display in data field MOV A, E STA C100H ; Store the 2-digit hex number in C100H MVI B, 01 CALL GTHEX ; Input a 2 digit number and display in ... Read More

We write a program in 8085 assembly language for implementing a decimal down counter (from 99 to 00). The program must be working in the following conditions.We load the accumulator with 99.Displaying the count value in the accumulator which is present in the accumulator. RST5.5 is in unmasked condition and the interrupt system gets enabled.The program is as follows:FILE NAME DOWNCNTR.ASM ORG C000H CURDT: EQU FFF9H UPDDT: EQU 06D3H RDKBD: EQU 0634H MVI A, 99H ; Initialize A with 99. REP: STA CURDT ; Store A value in CURDT. CALL UPDDT ; Display contents of CURDT in data field. MVI ... Read More

In 8255, there are two types of command words or control word are available. And they are −Mode definition control word andPort C bit set/reset control word.Both these are written to the control port only. From the point of view of the microprocessor there is a single 8-bit control port, which is selected when CS* = 0, WR* = 0, A1 = 1 and A0 = 1. But if we consider the architecture of 8255, internally there are two control ports, one for mode definition control and another for Port C bit set/reset control. The contents of the control port ... Read More

We write an 8085 assembly language program for finding the square of a single digit (0 to 9) using a look-up table for displaying a number and its square in the address field.FILE NAME MYSQR.ASM ORG C100H X: DB 00H, 01H, 04H, 09H, 16H, 25H, 36H, 49H, 64H, 81H ORG C000H CURAD: EQU FFF7H UPDAD: EQU 06BCH IBUFF: EQU FFFFH MVI A, 0EH ; Load A with 0000 1110B SIM ; Unmask RST5.5 i.e. enable keyboard interrupt. ; The next 4 instructions check if a key is pressed. If a key is ; pressed, ... Read More

We write an 8085 assembly language program just to simulate a stopwatch for displaying minutes and seconds in the address field. There exists a provision to stop the stopwatch, along with the display for continuation to show the time just previous to the stop command.FILE NAME STOPWACH.ASM PRESSING THE ‘VECT INTR’ KEY STOPS THE STOPWATCH, WITH STATIONARY DISPLAY ORG C000H CURAD: EQU FFF7H UPDAD: EQU 06BCH RESET: LXI H, 0000H REPEAT: SHLD CURAD CALL UPDAD; Display time present in HL in the address field MVI A, 00011011B SIM ; Unmask RST7.5, Reset RST7.5 flip flop EI ; Enable interrupt ... Read More

There are three modes of operation which are supported by 8255. We call them as mode 0, mode1 and mode 2.We call the mode 0 as the simple Input Output or the basic Input Output for performing the simplest mode of operation. Every ports of 8255 can be programmed to work in mode 0.We call mode 1 as the strobed Input Output or handshake Input Output. It is useful when data is supplied to the input device by the microprocessor at irregular interval of time. Finally, when the data is read by the processor the port informs the Input device ... Read More

Write an 8085 assembly language program to simulate the throw of a die using an interrupt.We have a counter for this program, which counts the ranges from 1 to 6, and again repeats the sequence of count in a matter which is endless in an infinite loop. The die throwing getting the head and tail probability gets simulated by pressing the key ‘Vect Intr’ on the keyboard. The branching of 8085 branches to RST7.5 ISS. Here, the current value of the counter gets is displayed in the data field, which controls and returns to the main program for the continuation ... Read More

 Let us say that the 8085 which is interrupted because of RST6.5 pin and has been branched to the ISS for the pin RST6.5. Then, except the DI instruction at the beginning of this ISS, all the interrupts gets disabled except TRAP. So, even if RST7.5 pin is in activated state in the middle of the execution of RST6.5 ISS, the interruption of 8085 will not occur due to RST7.5. Actually a higher priority interrupt is RST7.5, but the lower priority interrupt ISS cannot be interrupted by it of RST6.5. We solve this problem by specifically having the instruction which ... Read More