Assembly programming and Instruction of 8051

✏️Assembly programming and Instruction of 8051

👉Subroutine

👉Call instruction

👉Nested loop

✏️SUBROUTINE 

📌In assembly language programming it is common to have one main program and many sub routines that are called from the main program.

📌The is allows to make separate module of program known as subroutine. 

📌Each module can be tested separately and brought together in main program.

📌More importantly, in a large program the modules can be assigned to different programmers to shorten development time.

✏️CALL INSTRUCTIONS

👉LCALL (long call)

👉ACALL (absolute call)

📌LCALL (LONG CALL)

 👉It is a 3 byte instruction. 

👉The first byte is the opcode and second and third are used address of  target subroutine.

👉This can be used to call subroutines located anywhere within the 64K-byte address space of 8051.

👉When a subroutine is called, control is transferred to that subroutine, processor saves the program counter and begins to fetch instructions from new location.

👉 After execution the subroutine, thee instruction RET (return) control back to the caller. 

Syntax : LCALL LABEL

✏️ACALL (ABSOLUTE CALL) 

👉ACALL is a 2-byte instruction. 

👉Only 11 bits are used as address. 

👉While the target address of ACALL must be within a 2K-byte range. In variation of the 8051,  on-chip ROM is as low as 1K byte.

👉 In such cases, the use of ACALL instead of LCALL can save a number of bytes of ROM space.

Syntax : ACALL LABEL

✏️NESTED LOOPS

👉A loop within a loop, an inner loop within the outer one 

👉The first pass of outer loop triggers the inner loop which executes to completion. 

👉Then the second pass of outer loop of outer loop triggers inner loop again

👉This repeats till outer loop FINISHES. 

📌SYNTAX

for (initialize counter; test condition; ++ or –)

{

for (initialize counter; test condition; ++ or --)

{

.// inner loop

}

.//outer loop

}