The SSTL_15 library supports bidirectional single-ended and differential SSTL_15 signaling. The driver/receiver pairs, with embedded power cells, are supplied with a full complement of calibration, voltage reference, power, spacer, and adapter cells to assemble a pad ring by abutment. An included rail splitter allows isolated SSTL domains to be placed in the same pad ring with other power domains while maintaining continuous VDD/VSS in the pad ring for robust ESD protection.