Altera Designing With Low-Level Primitives Bedienungsanleitung PDF herunterladen (Seite 48)

2–26 Altera Corporation

Designing with Low-Level Primitives User Guide April 2007

Primitives

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 three ports (oe,

bidirin, and io) are connected. Also note that all parameters are

optional.

Example 2–17 shows a VHDL example of an ALT_BIDIR_BUF

component declaration.

slew_rate

Any legal slew rate value for the current device. This value must be a positive

integer (including 0).

enable_bus_hold Whether 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. This value is set as

the input as well as the output termination value for the current device. To set

separate input and output values, use the

input_termination and

output_termination parameters instead.

This parameter cannot be used with

input_termination or

output_termination.

input_termination

Any legal input on-chip-termination value for the current device. This parameter

cannot be used along with the “

termination” parameter.

Note: The Fitter ignores this parameter for Cyclone III devices.

output_termination

Any legal output on-chip-termination value for the current device. This

parameter cannot be used along with the “

termination” parameter.

Table 2–10. ALT_BIDIR_BUF Ports and Parameters (Part 2 of 2)

Port/Parameter Description/Value

1 2 ... 43 44 45 46 47 48 49 50 51 52 53 54 55 56

Keine Kommentare

Altera Designing With Low-Level Primitives Bedienungsanleitung Seite 48