Altera Designing With Low-Level Primitives - Manual (Page 33)

Altera Corporation 2–11
April 2007 Designing with Low-Level Primitives User Guide
Primitive Reference
ALT_INBUF_DIFF
This primitive allows you to name and connect positive and negative pins
when a differential I/O standard is used for an input pin. You can assign
I/O standard assignments, location assignments, termination
assignments, control bus hold circuitry, and enable weak pull up on the
input pins. An attempt to set any other parameter will result in an error.
Table 2–5 lists the ports and parameters of the ALT_INBUF_DIFF
primitive, and their respective descriptions and possible values.
Each parameter also accepts the value “none”. Assigning the value
“none” to any parameter is equivalent to not setting the parameter. Note
that the primitive requires that all three ports (
i, ibar, and o) are
connected. Also note that all parameters are optional.
Table 2–5. ALT_INBUF_DIFF Ports and Parameters
Port/Parameter Description/Value
Input Ports
i This port represents the positive pin of a differential I/O standard.
Connect this port either to the device’s input pin or to a wire to be connected to
an input pin. There must be no logic between the
i port and the device's input
pin. The input pin cannot have any other fan-out.
ibar This port represents the negative pin of a differential I/O standard.
Connect this port either to the device's input pin or to a wire to be connected to
an input pin. There must be no logic between the
ibar port and the chip input
pin. The input pin cannot have any other fan-out.
Output Ports
o Connect this port to the logic in the design to receive the input signal.
Parameter Name
io_standard Any legal differential I/O standard value.
location Any legal pin location for the current device.
enable_bus_hold An option to enable bus-hold circuitry. Legal values are “ on ” and “ off .”
weak_pull_up_resistor An option to enable the weak pull-up resistor. Current legal values are “ on ” and
“ off ”.
termination Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination. This
parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy II, and
Cyclone II.
Note: The Fitter ignores this parameter for Cyclone III devices.