Dear sir: Can I ask a question,I have a cpu like 8051 and stack point can locate external memory, can I use the C51 to define the stack point to extern memory or must be internal memory. Best Regard
The hardware SP register of the 8051 CPU can only address the internal RAM - see the Data Sheet. However, you can simulate an external stack in XDATA by making your functions reentrant - see the C51 Manual
There are today also several 8051 variants that allow to place stack in XDATA or extended memory spaces. For example Philips 80C51MX or Dallas 390/400.