Memory Test Program

I am working on a program that is supposed to test blocks of memory locations.

I need to write to memory, read it back and make sure that the write and the read are then the same.

My question is, How do I avoid writing over my code segment? Also I am supposed to implement a far call. It is my understanding that a far call is in another code segment. How do I avoid writing over this as well?

If anyone can help, thanks!