There are couple of dip switches on an Allen-Bradley PLC-5, and each of them outlines specific function for the PLC-5 to perform. These dip switches can be located on the side (denoted by B1) and bottom (denoted by S1) of PLC-5 CPU card.
This is where you would find the side dip swithes (B1).
Dip swithc B1 is for DH+ station number
Dip switch S2 is for communication type (RS232, RS422 or RS423)
The diagram below are from page (E-2, page 340)