Assuming you use a standard RS232 cable with DB9 connectors, the wire list would look like this.

DB9-F.2 RS232.TXD RS232.DIN RD2.P3.1
DB9-F.3 RS232.RXD RS232.ROUT RD2.P3.0
DB9-F.5 Ground
PSEN (pin 26) must be grounded before the board power is turned on.

DB9-F = DB9 Female connector
RS232 = RS232 transceiver
RD2 = T89C51RD2

I'm currently using a T89C51RD2 but unfortunately, I cannot give you the schematic. I hope the above wire list helps.

Good luck!
Patrick