The RS530 interface is a generic connector specification. It´s not an actual interface. The connector pinning can be used to support RS422, RS423, V.35 and X.21 to name the most popular ones.
25 pin D-SUB male connector at the DTE (Computer)
RS530 is just like RS422 and uses a differential signaling on a DB25 - RS232 format - EIA-530 Transmit (and the other signals) use a twisted pair of wires (TD+ & TD-) instead of TD and a ground reference as in RS232 or V.24. This interface is used for HIGH SPEED synchronous protocols. Using a differential signaling allows for higher speeds over long cabling. This standard is applicable for use at data signaling rates in the range from 20,000 to a nominal upper limit of 2,000,000 bits per second. Equipment complying with this standard, however, need not operate over this entire data signaling rate range. They may be designed to operate over a narrower range as appropriate for the specific application.
25 pin D-SUB female connector at the DCE (Modem)