The appendix of each products' OWNERS MANUAL has a wiring diagram of the required cable.

MAC use RSC15APL :
The MAC cable is a STANDARD MAC serial cable.

IMB PC use RSC15AT: ws $7.00 retail $10.50 SSI INV Item
The IBM PC AT cable is available from MCM Electronics 1 800 543 4330 (they have a min. order of $20.00 + ship) Part # 83-2330 $5.95 ea