C51: Stack Usage

Information in this article applies to:

• C51 All Versions

QUESTION

How does the C51 compiler use the stack?

ANSWER

The 8051 hardware stack is used for:

• Return addresses from function calls,
• Saving and restoring registers used in interrupts, and
• Saving and restoring intermediate results.

While the 8051 architecture restricts the stack to internal memory, it may be located at any point therein. The stack typically starts following the last individual variable allocation in internal memory and is free to grow "up" through whatever memory remains. C51 stack usage is minimal.

Automatic, local variables are overlaid in internal data memory using a strategy that maximizes memory utilization. This is similar to the method used by the Intel PL/M-51 programming language.

SEE ALSO

• C51: Modifying the Startup Routines
• C51: Setting Program Start Address
• C51: Avoiding Startup Initialization of Static Variables
• C51: Checking for Stack Underflow at Runtime
• C51: Stack and Reentrant Stack Symbolic Names
• C51: Stack Pointer Initialization in Startup Code
• C51: Calculating Stack Size
• C51: Locating the Stack after IDATA Variables

Last Reviewed: Thursday, February 25, 2021