HD IOB Features

IOSTANDARD Attribute

The IOSTANDARD attribute is available to choose the values for an I/O standard for all I/O buffers. The supported I/O standards are listed in the HD IOB Supported Standards section. The IOSTANDARD attribute uses the following syntax in the XDC file:

set_property IOSTANDARD value [get_ports port_name]

INTERNAL V_REF

The receivers for HSTL (HSTL_I_18 and DIFF_HSTL_I_18) and SSTL (SSTL18_I and DIFF_SSTL18_I) standards require a reference (V_REF) to define input switching thresholds. In HD IOB, these levels are internally provided at V_CCO/2. In HD IOB, V_REF is always internally generated and there are no attributes that must be set to enable the reference. It is automatically inferred when a input that requires V_REF is used in a design. See the HD IOB Supported Standards section for the standards that use internal V_REF.

Drive Strength Control

LVCMOS drivers (LVCMOS33, LVCMOS25, and LVCMOS18) and LVTTL drivers support output drive strength control to size the driver output strength to the load driven. Assigning the DRIVE property 4, 8, or 12 ensures that the HD IOB driver can meet valid logic thresholds for loads of 4 mA, 8 mA, or 12 mA, respectively. The DRIVE attribute uses the following syntax in the XDC file:

set_property DRIVE value [get_ports port_name]

Slew Control

All LVCMOS (LVCMOS33, LVCMOS25, and LVCMOS18) and LVTTL drivers support FAST and SLOW slew rate options. These options can be used to optimize the driver edge rate. The SLEW attribute uses the following syntax in the XDC file:

set_property SLEW value [get_ports port_name]

Uncalibrated On-Die Termination (ODT)

The HD IOB provides uncalibrated input split termination for HSTL (HSTL_I_18 and DIFF_HSTL_I_18) and SSTL (SSTL18_I and DIFF_SSTL18_I) I/O standards. The allowed values for the ODT attribute are RTT_48 and RTT_NONE. It defines the equivalent termination to be either 48Ω or to explicitly disable the ODT. The ODT attribute uses the following syntax in the XDC file:

set_property ODT value [get_ports port_name]

PULLUP, PULLDOWN, KEEPER

All HDIO pins can enable a weak internal PULLUP bias to V_CCO, a weak internal PULLDOWN to GND, or a weak internal KEEPER circuit that will both pull-up to V_CCO and pull-down to GND based on the last driven pin voltage. This feature can be invoked by adding the following possible constraint values for the PULLTYPE attribute to the relevant net of the buffers:

• NONE
• PULLUP
• PULLDOWN
• KEEPER

These attributes use the following syntax in the XDC file:

set_property PULLTYPE value [get_ports port_name]