Altera Designing With Low-Level Primitives - Manual (Page 37)

Altera Corporation 2–15
April 2007 Designing with Low-Level Primitives User Guide
Primitive Reference
Table 2–7 lists the ports and parameters of the ALT_OUTBUF_TRI_DIFF
primitive, and their respective description 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
the default. Assigning –1 to slew_rate is equivalent to not setting the
parameter. Note that the primitive requires that all four ports ( i, oe, o,
and obar) are connected. Also note that all parameters are optional.
Example 2–11 shows a Verilog HDL example and Example 2–12 shows a
VHDL example of an ALT_OUTBUF_TRI_DIFF.
Table 2–7. ALT_OUTBUF_TRI_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.
oe Connect this port to the tri-state output enable logic.
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.