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

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

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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