2.3.3.2 Using an I/O Register
To access the I/O registers, registers must be instantiated in the netlist and
then connected to the I/Os. Usage of each I/O register (register combining) is
individually controlled and can be selected/deselected using the PinEditor tool in the
Designer software. I/O register combining can also be controlled at the device level,
affecting all I/Os. The I/O register option is deselected by default in any given
design.4
In addition, Designer software provides a global option to enable/disable the usage of registers in the I/Os. This option is design-specific. The setting for each individual I/O overrides this global option. Furthermore, the global set fuse option in the Designer software, when checked, causes all I/O registers to output logic High at device power-up.
1
Please note that register combining for multi fanout nets is not supported.