LVDCI

Using these I/O buffers configures the outputs as controlled impedance drivers. The receiver of low-voltage digitally controlled impedance (LVDCI) is identical to an LVCMOS receiver. Some I/O standards, such as LVCMOS, must have a drive impedance that matches the characteristic impedance of the driven line. The HP I/O banks provide a controlled impedance output driver to provide series termination without external-source termination resistors.

Source termination is controlled using the OUTPUT_IMPEDANCE attribute. The exact value of the impedance is determined by the OUTPUT_IMPEDANCE attribute and an external 240 Ω resistor on the VRP pin. The only valid value of this attribute for LVDCI standards is RDRV_48_48, which corresponds to a 48 Ω setting.

Sample circuits illustrating both unidirectional and bidirectional topologies for a controlled impedance driver are shown in This Figure and This Figure . The DCI I/O standards supporting a controlled impedance driver are: LVDCI_15 and LVDCI_18.

Table: Allowed Attributes for the LVDCI I/O Standards details the allowed attributes that can be applied to the LVDCI I/O standard. This standard is available in the HP I/O banks. Support is implied for primitives that are derivatives of the primitives listed in Table: Allowed Attributes for the LVDCI I/O Standards (for example: *_DIFF_OUT, *_DCIEN, *_IBUFDISABLE, or *_INTERMDISABLE). Refer to the SelectIO Interface Primitives section for all supported derivatives.