Texas Instruments MSC1210 manual Label and instruction

Models: MSC1210

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Syntax

In summary, a typical 8052 assembly language line might appear as:

MYLABEL: MOV A,#25h ;This is just a sample comment

In this line, the label is MYLABEL. This means that if subsequent instructions in the program need to make reference to this instruction, they may do so by referring to MYLABEL, rather than the memory address of the instruction.

The 8052 assembly language instruction in this line is MOV A,#25h. This is the actual instruction that the assembler will analyze and assemble into the two bytes 74H 25H. The first number, 74H, is the 8052 machine language instruc- tion (opcode) “MOV A,#dataValue”, which means “move the value dataValue into the accumulator.” In this case, the value of dataValue will be the value of the byte that immediately follows the opcode. We want to load the accumulator with the value 25H and the byte following the opcode is 25H. As you can see, there is a one-to-one relationship between the assembly language instruction and the machine language code that is generated by the assembler.

Finally, the instruction above includes the optional comment “;This is just a sample comment”. The comment must always start with a semicolon. The semicolon tells the assembler that the rest of the line is a comment that should be ignored by the assembler.

All fields are optional and the following are also alternatives to the above syntax:

Label only:

LABEL:

Label and instruction:

LABEL: MOV A,#25h

Instruction and comment:

MOV A,#25h ;This is just a comment

Label and comment:

LABEL: ;This is just a comment

Comment only:

;This is just a sample comment

All of the above permutations are completely valid. It is up to you as to which components of the assembly language syntax are used. However, when used, they must follow the above syntax and be in the correct order.

Note:

It does not matter what column each field begins in. That is, a label can start at the beginning of the line or after any number of blank spaces. Likewise, an instruction may start in any column of the line, as long as it follows any label that is also on that line.

8052 Assembly Language

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Page 197
Image 197
Texas Instruments MSC1210 manual Label and instruction