Assembly language, Assembly Language

Assembly Language:

Inside the 8085, instructions are really stored like binary numbers, not a very good manner to look at them and very difficult to decipher. An assembler is a program that permits you to write instructions in, more or less, English form, much more simply read and understood, and after that converted or assembled into hex numbers and at last into binary numbers.

The program is written with a text editor (NOTEPAD or similar), saved like an ASM file, and then assembled by the assembler (TASM or MASM or similar) program. The end result is an OBJ file you download to the 8085. Here is an instance of the problem of adding 2 plus 2 :

mvi A,2; move 2 into the A register

mvi B,2; move 2 into the B register

add B; add reg. B to reg. A, store result in reg. A

The first line moves a 2 into a register A. The second line moves a 2 into a register B. it is all the data we require for the program. The third line adds up the accumulator with register B and holds the result back into the accumulator, destroying the 2 that were originally in it. The accumulator contains a 4 in it now and B still contains a 2 in it. In the program above all text after the ';' are treated as comments, and not executed. It is a very significant habit to acquire.

Assembly language follows some rules that we shall describe as they come up. With most of the instructions, especially those including data transfer, the instruction is first, followed by at least 1 space, after that the destination followed through a comma, and then the source. The destination is where the result of the instruction shall end up and the source is where the data is coming from.

Next we shall read a switch, and light an LED if the switch is pressed. This happens quite frequently in your lab experiments. Bit 0 of Port 0 shall be the switch. While the switch is closed or pressed, bit 0 will be a 1, and if the switch is open or not pressed, bit 0 will be a 0. Bit 0 of Port l is the LED. If bit 0 is a 0 the LED is off and if bit 0 is a 1, the LED shall be on. All the other bits of reg. A shall be ignored and assumed to be all 0's, for the sake of discussion

Start

IN         0          ; read Port 0 into reg. A

CMP    1          ;compare reg. A with the value 1

JNZ      start     ; jump to start if the comparison does not yield 0

OUT     1          ; send a 1 to Port 1, turning the LED on

JMP     start

 

The first line has something new. It's called as a label. In this case it is start:. A label is a manner of telling the assembler that this line has a name that may be referred to later to get back to it. All of the labels are followed by the symbol:, that tells the assembler that it is a label. In the first line we also read the switch by reading Port and putting it into the accumulator. Register. A is the only register that may read in/send out data using ports or perform compares. Therefore, we need not write 'A' in the command it's implied.

Posted Date: 2/7/2013 5:06:04 AM | Location : United States







Related Discussions:- Assembly language, Assignment Help, Ask Question on Assembly language, Get Answer, Expert's Help, Assembly language Discussions

Write discussion on Assembly language
Your posts are moderated
Related Questions
I/O interface I/O  devices such as displays and keyboards  establish  communication of computer with outside world. Devices may be interfaced in 2 ways Memory mapped I/O and I/

SCAS : Scan String Byte or String Word:- This instruction scans a string of words or byte for an operand word or byte specified in the register AL or  register AX. The string i


programs

The addressing modes for the sequential control transfer instructions are described below:   1. Immediate: Immediate data is a part of instruction,in this type of addressin

calculate the number of one bits in bx and complement an equal number of least significant bits in ax hint use the xor instruction

#write a program 8086 to find the largest number

AND: Logical AND: This instruction bit by bit ANDs the source operand that might be an immediate, or a memory location or register to the destination operand that might be a memor


Why is the capability to relocate processes desirable?