I am trying to implement the memory chip but I don't understand what this means,
* Access to address>0x6000 is invalid. Access to any address in
* the range 0x4000-0x5FFF results in accessing the screen memory
* map. Access to address 0x6000 results in accessing the keyboard
* memory map.
So the "0x" prefix means that the number following is expressed in hexadecimal (also known as base-16) in which the 16 digits are represented by the ten decimal digit symbols (i.e., '0' through '9') followed by the first six letters of the alphabet (i.e., 'A' through 'F' -- upper/lower case doesn't matter).
So just like the decimal representation 314 means
314 = (3 x 10^2) + (1 x 10^1) + (4 x 10^0)
the hexadecimal representation 0x5FFF means
0x5FFF = (5 x 16^3) + (15 x 16^2) + (15 x 16^1) + (15 x 16^0) = 24,575