The part number of the cable required to connect a PC running Zelio Soft2 programming software (SR2SFT02) to the USB communication port on an SR2 or SR3 programmable relay is SR2USB01.
The communication lead SR2USB01 is 3m long and has a USB connector on one end and a dedicated Zelio connector on the other. You can find the datasheet by clicking on the part number above.