Altera Designing With Low-Level Primitives Bedienungsanleitung PDF herunterladen (Seite 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

Connect this port to the logic in the design that generates the output signal.

Connect this port to the tri-state output enable logic.

Output Ports

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.

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