C51: Mixing Memory Models and Memory Areas

Information in this article applies to:

• C51 Version 5.50

QUESTION

We have a large memory configuration (external RAM of 64K code and 64K XData). We would like to use the external data for buffers, queues, and so on.

Is there a compiler option to use the internal RAM (256 -32 bytes) for our stack? We do not want to use the simulated stack because of inefficiency.

ANSWER

The compiler is completely flexible in where you locate variables, buffers, reentrant stacks, and so on. You may specify different memory models for each function in your program, different memory models for reentrant functions, and for each variable. For example:

• void func (void) large -- large memory model function - vars stored in xdata
• void func (void) small -- small memory model function - vars stored in data
• void func (void) small reentrant -- reentrant function using the small memory model reentrant stack
• http://www.keil.com/support/man/docs/c51/c51_le_memmodels.htm
• char xdata x; -- char in xdata
• int code y; -- int in code (EPROM)

SEE ALSO

• http://www.keil.com/support/docs/995.htm
• Memory Models

Last Reviewed: Thursday, February 25, 2021