I am working on a an 8051 based light tracker system whose hardware I have prepared in PCB, It has a very simple mapping in which two 8255 chips have been mapped into the conventional addressing area on the 8051 and should be accessed by instructions such as MOVX @DPTR,A or the like, now it's very easy to write the code to handle them in assembly ( I have done this and it has worked) but when working with KEIL and writing C51 and trying to define them at absolute memory addresses, I have failed. I am not very familiar with KEIL and I don't know about the setup that I have to make when working with external RAM and absolute memory addresses, I have surfed the web for documentation for KEIL on that subject and I have found two big manuals for KEIL in which these issues have not been properly addressed, I would be happy if I am provided with sufficient documentation or guidance about this. thanks