Hallo everybody, can I overwrite the SFR and write other datas like constants. For example can I delete the ASC Registers because I don't need them?
Unless the datasheet clearly specifies that something can be used as a scratchpad, such experiments are at best ugly and confusing for anyone trying to maintain the program, and at worst they'll cause true nightmares. If you really need additional space, maybe you should look for a different chip.
I must use these controller and I can not add a external RAM. I need more free space for all my variables. What can I do to get more space.
What can I do to get more space. If you run out of RAM (IDATA/XDATA) on a '51, you either need to optimize your programs memory usage (by changing your code and/or using compiler/linker features like memory overlaying) or pick a different device. Misusing SFRs as additional registers requires that you know the '51 architecture and your particular device inside out. And if you do the latter, you will probably not resort to this technique since you know that it can only lead to nightmares.
what is the controller you are using? Is it really contains a very small RAM to hold your variables??? Can you roughly say how much bytes of variables you are using?