# Using port 0 in AT89C52 without pull up resistors

So at my university professor gave us following scheme to program this double 7 segment display on the right. At start I tried to simply adress it using P0=(someData) although it didn't work. Then I asked my friend how to do it and he said that during lecture professor said that if you want to make it to work you have to adress left part of display as:

unsigned char xdata left _at_ 0xFE00;


and right part of display as:

unsigned char xdata right _at_ 0xFD00;


The question I'm having is why specifically those adresses make it work for port 0? I tried to use other adresses such as 0xFA00 and 0xFB00 and it didn't work. I've also read specifications, documentations of programming those microcontrollers although I didn't find anything.

Can someone explain why it works like that? It apparently is some trick and I'm reaaally curious.