PSEN Pin when interfacing external memory in Harvard Architecture 8051
This pdf provides diagrams on interfacing the 8051 to 2732 EPROM and also 8155 external RAM: http://www.cs.ucr.edu/~ehwang/courses/cs120b/8051.pdf 

Also got this from GoogleBooks: https://books.google.com.ng/books?id=K2qH4gW-fcUC&amp;pg=PA134&amp;lpg=PA134&amp;dq=2732+EPROM+psen&amp;source=bl&amp;ots=KmXZPDtQcq&amp;sig=Zae0KdCCTRZfmQEwX8LFlaxpPsY&amp;hl=en&amp;sa=X&amp;ved=0ahUKEwiWg72YiqPKAhWH8RQKHbXTB1gQ6AEIRzAI



Good luck.