The IOBUF primitive is needed when bidirectional signals require both an input buffer and a 3-state output buffer with an active-High 3-state T pin. This Figure shows a generic IOBUF. A logic-High on the T pin disables the output buffer. When the output buffer is 3-stated (T = High), the input buffer and any on-die receiver termination (uncalibrated or DCI) are ON. When the output buffer is not 3-stated (T = Low), any on-die receiver termination (uncalibrated or DCI) is disabled.