Altera Designing With Low-Level Primitives - Manual (Page 35)

Altera Corporation 2–13
April 2007 Designing with Low-Level Primitives User Guide
Primitive Reference
ALT_OUTBUF_DIFF
This primitive allows you to name and connect positive and negative pins
when a differential I/O standard is used for an output pin. You can assign
I/O standard, location, drive strength (current strength), slew rate, and
termination assignments, control bus hold circuitry, and enable weak
pull-up resistor on the output pins. An attempt to set any other parameter
will result in an error.
Table 2–6 lists the ports and parameters of the ALT_OUTBUF_DIFF
primitive, and their respective descriptions and possible values.
Each parameter except slew_rate also accepts the value “none”.
Assigning the value “none” to any such parameter is equivalent to not
setting the parameter. The parameter
slew_rate accepts the value –1 as
Table 2–6. ALT_OUTBUF_DIFF Ports and Parameters
Port/Parameter Description/Value
Input Ports
i Connect this port to the logic in the design that generates the output signal.
Output Ports
o This port represents the positive pin of a differential I/O standard.
Connect this port to the device’s output pin or a wire to be connected to the
device’s output. There must be no logic between the
o port and the chip output
pin. This port cannot have multiple fan-outs.
obar This port represents the negative pin of a differential I/O standard.
Connect this port to the device's output pin or a wire to be connected to the
device's output. There must be no logic between the
obar port and the chip
output pin. This port cannot have multiple fan-outs.
Parameter Name
io_standard Any legal differential I/O standard value.
current_strength Any legal value of the current_strength_new QSF assignment.
location Any legal pin location for the current device.
slew_rate Any legal slew rate value for the current device. This value must be a positive
integer (including
0 ).
enable_bus_hold Whether or not to enable bus-hold circuitry. Current legal values are “ on ” and
“ off ”.
weak_pull_up_resistor Whether or not 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.