Quartus II Settings File Reference Manual - Altera

6–228 Chapter 6: Fitter Assignments
OUTPUT_ENABLE_GROUP
OUTPUT_ENABLE_GROUP
Type
Assigns an output enable group number for the specified node. Turning on this option
directs the Fitter to view the specified nodes as an output enable group so as not to
violate the requirements for the maximum number of pins driving out of a VREF
group when a voltage-referenced input pin or bidirectional pin is present. For
bidirectional pins, the Fitter determines all possible pins that may potentially drive
out when any bidirectional pin is driving in by looking at the output enable of all the
bidirectional pins in the VREF group. This behavior can result in the VREF group
exceeding the maximum number of outputs and result in a no fit. Turning on the
Output Enable Group option allows you to specify an output enable group for
specific pins, thus allowing you to specify which pins in the design are driving in and
out at the same time. The Fitter only considers pins as potential outputs when they are
in separate output enable groups or when they are not in an output enable group; by
specifying an output enable group, you can lower the total number of outputs in the
VREF group when any pin is driving in. As a result, the Fitter does not count all of the
potential outputs of the bidirectional pins and the number of outputs in the VREF
group remains in the legal range. You should turn on this option when the Fitter
cannot detect the output enable group of the pins in the VREF group, for example
when the output enables come from a state machine or complex logic. For detailed
information on the number of outputs supported by a VREF group, refer to the
respective device family data sheet.
Integer
Device Support
This setting can be used in projects targeting the following device families:
■ Arria GX
■ Arria II GX
■ Arria II GZ
■ Arria V
■ Cyclone
■ Cyclone II
■ Cyclone III
■ Cyclone III LS
■ Cyclone IV E
■ Cyclone IV GX
■ Cyclone V
■ HardCopy II
■ HardCopy III
■ HardCopy IV
Quartus Settings File June 2012 Altera Corporation
Reference Manual