Every HD I/O bank contains 24 I/O pins. When defined as single-ended standards, HD I/O pins support input, output, and bidirectional operating modes. Paired I/O pins can be used to support differential standard functionality. For pseudo-differential standards, like DIFF_SSTL15, input, output, and bidirectional support is available. True differential standards, like LVDS_25, can only function as an input buffer.