Altera Designing With Low-Level Primitives User Manual

Designing with Low-Level Primitives

101 Innovation Drive
San Jose, CA 95134
[phone]
www.altera.com

User Guide

Software Version 7.1
Document Version: 3.0
Document Date: April 2007

Copyright © 2007 Altera Corporation. All rights reserved. Altera, The Programmable Solutions Company, the stylized Altera logo, specific device des­ignations, and all other words and logos that are identified as trademarks and/or service marks are, unless noted otherwise, the trademarks and
service marks of Altera Corporation in the U.S. and other countries. All other product or service names are the property of their respective holders. Al­tera products are protected under numerous U.S. and foreign patents and pending applications, maskwork rights, and copyrights. Altera warrants
performance of its semiconductor products to current specifications in accordance with Altera's standard warranty, but reserves the right to make
changes to any products and services at any time without notice. Altera assumes no responsibility or liability arising out of the ap­plication or use of any information, product, or service described herein except as expressly agreed to in writing by Altera
Corporation. Altera customers are advised to obtain the latest version of device specifications before relying on any published in­formation and before placing orders for products or services.

UG-83105-3.0

ii MegaCore Version a.b.c variable Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

Contents

About this User Guide .............................................................................. v

How to Contact Altera .............................................................................................................................. v

Typographic Conventions ...................................................................................................................... vi

Chapter 1. Low-Level Primitive Design

Introduction ............................................................................................................................................ 1–1

Low-Level Primitive Examples ........................................................................................................... 1–2

LCELL Primitive ............................................................................................................................... 1–2

Using I/Os ......................................................................................................................................... 1–6

Using Registers in Altera FPGAs ................................................................................................... 1–7

Creating Memory for Your Design ................................................................................................ 1–9

Look-Up Table Buffer Primitives .................................................................................................1–13

Chapter 2. Primitive Reference

Primitives ................................................................................................................................................ 2–1

ALT_INBUF ...................................................................................................................................... 2–1

ALT_OUTBUF .................................................................................................................................. 2–3

ALT_OUTBUF_TRI .......................................................................................................................... 2–6

ALT_IOBUF ....................................................................................................................................... 2–8

ALT_INBUF_DIFF ......................................................................................................................... 2–11

ALT_OUTBUF_DIFF ..................................................................................................................... 2–13

ALT_OUTBUF_TRI_DIFF .............................................................................................................2–14

ALT_IOBUF_DIFF .......................................................................................................................... 2–19

ALT_BIDIR_DIFF ........................................................................................................................... 2–22

ALT_BIDIR_BUF ............................................................................................................................ 2–25

LCELL .............................................................................................................................................. 2–27

DFF ................................................................................................................................................... 2–28

CARRY and CARRY_SUM ........................................................................................................... 2–29

CASCADE ....................................................................................................................................... 2–30

LUT_INPUT .................................................................................................................................... 2–31

LUT_OUTPUT ................................................................................................................................ 2–32

Synthesis Attributes ............................................................................................................................ 2–33

Altera Corporation iii

Contents

iv Altera Corporation
Designing with Low-Level Primitives User Guide

About this User Guide

Document Revision History

Date and

Document

Version

April 2007
v3.0

May 2006
v2.0

October 2005
v1.0

Made changes to the Guide:

● Added examples 1–8, 2–4, 2–6, 2–8

● Added these new sections:

“ALT_INBUF_DIFF” on page 2–11
“ALT_OUTBUF_DIFF” on page 2–13
“ALT_OUTBUF_TRI_DIFF” on page 2–14
“ALT_IOBUF_DIFF” on page 2–19
“ALT_BIDIR_DIFF” on page 2–22
“ALT_BIDIR_BUF” on page 2–25

● Removed most of the “Synthesis Attributes” on page 2–33

section, replaced with a reference to the Quartus II
Handbook.

Technical changes to coincide with changes to the Quartus II
software 6.0.0 release

Initial Release

How to Contact Altera

The table below shows the revision history for this document.

Changes Made Summary of Changes

Technical changes to
coincide with changes to
the Quartus II software

7.0.0 release

—

—

For the most up-to-date information about Altera® products, go to the
Altera world wide web site at www.altera.com. For technical support on
this product, go to www.altera.com/mysupport. For additional
information about Altera products, consult the sources shown below.

Information Type Resource

Technical support www.altera.com/mysupport/

Product literature www.altera.com

Altera literature services [e-mail] (1)

FTP site ftp.altera.com

Note to table:

(1) You can also contact your local Altera sales office or sales representative.

Altera Corporation v
April 2007 Designing with Low-Level Primitives User Guide

Typographic Conventions

Typographic

This document uses the typographic conventions shown below.

Conventions

Visual Cue Meaning

Bold Type with Initial
Capital Letters

bold type External timing parameters, directory names, project names, disk drive names,

Italic Type with Initial Capital
Letters

Italic type Internal timing parameters and variables are shown in italic type.

Initial Capital Letters Keyboard keys and menu names are shown with initial capital letters. Examples:

“Subheading Title” References to sections within a document and titles of on-line help topics are

Courier type Signal and port names are shown in lowercase Courier type. Examples: data1,

1., 2., 3., and
a., b., c., etc.

● • Bullets are used in a list of items when the sequence of the items is not important.

■

v The checkmark indicates a procedure that consists of one step only.
1 The hand points to information that requires special attention.

c

w

r The angled arrow indicates you should press the Enter key.

f The feet direct you to more information on a particular topic.

Command names, dialog box titles, checkbox options, and dialog box options are
shown in bold, initial capital letters. Example: Save As dialog box.

filenames, filename extensions, and software utility names are shown in bold
type. Examples: f

Document titles are shown in italic type with initial capital letters. Example: AN

75: High-Speed Board Design.

Examples: t

Variable names are enclosed in angle brackets (< >) and shown in italic type.
Example: <file name>, <project name>.pof file.

Delete key, the Options menu.

shown in quotation marks. Example: “Typographic Conventions.”

PIA

, \qdesigns directory, d: drive, chiptrip.gdf file.

MAX

, n + 1.

tdi, input. Active-low signals are denoted by suffix n, e.g., resetn.

Anything that must be typed exactly as it appears is shown in Courier type. For
example:
actual file, such as a Report File, references to parts of files (e.g., the AHDL
keyword
Courier.

Numbered steps are used in a list of items when the sequence of the items is
important, such as the steps listed in a procedure.

A caution calls attention to a condition or possible situation that can damage or
destroy the product or the user’s work.

A warning calls attention to a condition or possible situation that can cause injury
to the user.

c:\qdesigns\tutorial\chiptrip.gdf. Also, sections of an

SUBDESIGN), as well as logic function names (e.g., TRI) are shown in

vi Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

1. Low-Level Primitive Design

Introduction

Your hardware description language (HDL) coding style can have a
significant effect on the quality of results that you achieve for
programmable logic designs. Although synthesis tools optimize HDL
code for both logic utilization and performance, sometimes the best
optimizations require engineering knowledge of the design. Therefore, it
is important to consider the HDL coding style that you adopt when
creating your programmable logic design.

Low-level HDL design is the practice of using low-level primitives and
assignments in your HDL code to dictate a particular hardware
implementation for a piece of logic. Low-level primitives are small
architectural building blocks that assist you in creating your design. With
the Quartus
design techniques that can help you to achieve better resource utilization
or faster timing results.

Using low-level primitives in your design enables you to control the
hardware implementation for a cone of logic in your design. These cones
can be as small as an LCELL instantiation, which prevents the Quartus II
synthesis engine from performing optimizations, to larger, more complex
examples that specify the encoding method for a finite state machine
(FSM).

The Quartus II software can synthesize and place and route designs that
instantiate low-level primitives. This user guide describes the support
that the Quartus II software offers for creating a design with primitives
and includes the definition of each primitive, usage guidelines, and
example designs.

®

II software, you have the option of using low-level HDL

Using the Quartus II software, you can instantiate a Quartus II primitive
into your HDL design. The source files for Quartus II primitives are built
into the Quartus II software.

Altera Corporation 1–1
April 2007

Low-Level Primitive Examples

Example 1–1 is a small Verilog example that shows an instantiation of a

DFF primitive and an ALT_OUTBUF_TRI primitive.

Example 1–1. Instantiation of a DFF Primitive and alt_outbuf_tri Primitive, Verilog

module compinst (data, clock, clearn, presetn,

input data, clock, clearn, presetn, a, b;
output q_out, t_out;

dff dff_inst (.d (data), .q (q_out), .clk (clock),

//dff is a primitive

alt_outbuf_tri tri_inst (.i(b), .oe(a), .o(t_out))
// alt_outbuf_tri is a primitive

endmodule

a, b, q_out, t_out);

.clrn(clearn),.prn (presetn));

Low-Level
Primitive
Examples

The following sections provide examples of how you can implement
low-level primitives:

■ “LCELL Primitive”

■ “Using I/Os” on page 1–6

■ “Using Registers in Altera FPGAs” on page 1–7

■ “Creating Memory for Your Design” on page 1–9

■ “Look-Up Table Buffer Primitives” on page 1–13

For detailed specification of the primitive’s ports used in these sections,
refer to “Primitives” on page 2–1.

LCELL Primitive

The LCELL primitive allows you to break up your design into
manageable parts and prevents the Quartus II synthesis engine from
merging logic. This is especially useful when you are trying to debug
your design at the implementation level.

1–2 Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

In Example 1–2, the LCELL primitive separates the logic in your design.
The first code example and the resulting view from the Quartus II
Technology Map Viewer (Figure 1–1) show that the logic is merged
during the synthesis process.

Example 1–2. LCELL Primitive Separates Logic

module logic_merge(

clk,
addr,
data,
dataout

);

input clk;
input [3:0] addr;
input [2:0] data;
output[2:0] dataout;
reg [2:0] dataout;

wire temp_0;
wire temp_1;
wire temp_2;
wire temp_3;
wire temp_4;
wire temp_5;
wire temp_6;

Low-Level Primitive Design

assign temp_3 = addr[0] & addr[1] & addr[2] & addr[3];
assign temp_4 = addr[3] & addr[2] & addr[1] & addr[0];
assign temp_1 = addr[1] & addr[2] & addr[3];
assign temp_2 = temp_1 & addr[0];
assign temp_5 = temp_2 & data[0];
assign temp_6 = temp_3 & data[1];
assign temp_0 = temp_4 & data[2];
always@(posedge clk)
begin

dataout[2] <= temp_0;

end

always@(posedge clk)
begin

dataout[0] <= temp_5;

end

always@(posedge clk)
begin

dataout[1] <= temp_6;

end

endmodule

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April 2007 Designing with Low-Level Primitives User Guide

Low-Level Primitive Examples

Figure 1–1. Logic Merged During the Process

By strategically placing the LCELLs, you can control how the Quartus II
synthesis engine splits your design into logic cells. This typically causes
your design to use more logic resources, so this primitive should be used
with care. In the following example, and the resulting view from the
Quartus II Technology Map Viewer (Figure 1–2), three LCELL primitive
instantiations are introduced between the combinational logic. Note that
“LCELL” is also the name that the Technology Map Viewer gives to the
logic cells in some device families, as shown in the figure.

1–4 Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

In Example 1–3, the address decoder logic is not merged with the
registers in the design.

Example 1–3. Address Decoder Logic Not Merged with Registers

module comb_logic_with_lcells(

clk,
addr,
data,
dataout

);

input clk;
input[3:0] addr;
input [2:0] data;
output [2:0] dataout;
reg [2:0] dataout;
wire temp_0;
wire temp_1;
wire temp_2;
wire temp_3;
wire temp_4;
wire temp_5;
wire temp_6;
wire temp_7;
wire temp_8;
wire temp_9;
assign temp_1 = addr[0] & addr[1] & addr[2] & addr[3];
assign temp_3 = temp_4 & addr[0];
assign temp_8 = temp_5 & data[0];
assign temp_9 = temp_6 & data[1];
assign temp_0 = temp_7 & data[2];
assign temp_4 = addr[1] & addr[2] & addr[3];
assign temp_2 = addr[3] & addr[2] & addr[1] & addr[0];
lcell inst1(.in(temp_1),
.out(temp_6));
lcell inst2(.in(temp_2),
.out(temp_7));
lcell inst3(.in(temp_3),
.out(temp_5));

Low-Level Primitive Design

always@(posedge clk)
begin

dataout[2] <= temp_0;
end
always@(posedge clk)
begin

dataout[0] <= temp_8;
end
always@(posedge clk)
begin

dataout[1] <= temp_9;
end
endmodule

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April 2007 Designing with Low-Level Primitives User Guide

Low-Level Primitive Examples

Figure 1–2. LCELL Primitive Instantiations

Using I/Os

With I/O primitives, you can make I/O assignments in your HDL file
instead of making them through the Assignment Editor in the Quartus II
software. Example 1–4 describes how to make an I/O standard
assignment to an input pin using the ALT_INBUF primitive in Verilog
HDL.

Example 1–4. Making an I/O Standard Assignment to an Input Pin Using the ALT_INBUF Primitive, Verilog

module io_primitives (data_in, data_out);

input data_in;
wire internal_sig;

output data_out;

alt_inbuf my_inbuf (.i(data_in), .o(internal_sig));

defparam my_inbuf.io_standard="1.8 V HSTL Class I";

assign data_out = !internal_sig;

endmodule

1–6 Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

Low-Level Primitive Design

For detailed specifications of the primitive’s ports used in these sections,
refer to “Primitives” on page 2–1.

I/O Attributes

There are no primitives available to define an I/O register that can be
implemented as a fast input, fast output, or fast output enable register.
However, registers associated with an input or output pin can be moved
into I/O registers using the following assignments in the Quartus II
software for those I/O pins:

■ fast_input_register

■ fast_output_register

■ fast_output_enable_register

These assignments can be set by HDL synthesis attributes. Example 1–5
illustrates the fast_output_register synthesis attribute.

Example 1–5. The fast_output_register Synthesis Attribute

module fast_output(i,clk,o);

input i;

output o;

reg o /* synthesis altera_attribute = ”FAST_OUTPUT_REGISTER”

=ON */;
always @(posedge clk)
begin

o <= i;
end

endmodule

1 For more information, refer to “Synthesis Attributes” on

page 2–33.

Using Registers in Altera FPGAs

The building blocks of FPGA architectures contain a combinational
component along with a register component. Each register component in
an Altera FPGA provides a number of secondary control signals (such as
clear, reset, and enable signals) that you can use to implement
control logic for each register without the use of extra logic cells. Device
families vary in their support for secondary signals, so you must consult
the device family data sheet to verify which signals are available in your
target device. Download the device family data sheets from the Literature
section of www.altera.com.

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April 2007 Designing with Low-Level Primitives User Guide

Low-Level Primitive Examples

Inferring Registers Using HDL Code

To make the most efficient use of the signals in the device, your HDL code
should match the device architecture as closely as possible. Because of the
layout of the architecture, the control signals have a certain priority.
Therefore, your HDL code should follow that priority whenever possible.
If you do not follow the signal priority, your synthesis tool emulates the
control signals using additional logic resources. Therefore, creating
functionally correct results is always possible. However, if your design
requirements are flexible (in terms of which control signals are used and
in what priority), you can match your design to the target device
architecture to achieve the optimal performance and logic utilization
results.

There are certain cases where using extra logic resources to emulate
control signals can have an unintended impact. For example, a

_enable signal has priority over a synchronous_reset or a

clock
clear signal in the device architecture. The clock

disables the clock line in the logic array block (LAB), and the sclr signal
is synchronous. In the device architecture, the synchronous clear takes
effect only when a clock edge occurs.

If you code a register with a synchronous clear signal that has
priority over a clock enable signal, the software must emulate the
clock enable functionality using data inputs to the registers. Because the
signal does not use the clock enable port of a register, you cannot
apply a Clock Enable Multicycle constraint. In this case, following the
priority of signals available in the device is clearly the best choice for the
priority of these control signals because using a different priority causes
unexpected results with an assignment to the clock enable signal.

_enable signal

The signal order is the same for all Altera device families, although, as
mentioned earlier, not all device families provide every signal. In general,
use the signal order shown in Tab le 1– 1 .

Table 1–1. Signal Order (from Highest to Lowest Priority)

Priority Signal

1

2

3

4

5

6

7

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Designing with Low-Level Primitives User Guide April 2007

Asynchronous clear

Preset

Asynchronous load

Enable

Synchronous clear

Synchronous load

Data in

Low-Level Primitive Design

The sclr signal is not inferred by Quartus Integrated Synthesis when
there are a large number of registers with different sclr signals.This
behavior makes it easier for the fitter to successfully route the design. If
you would like to force the use of the sclr signals, you can use the
following Quartus II synthesis settings.

f For more details about these and other synthesis settings, refer to the

Quartus II Integrated Synthesis chapter in volume 1 of the Quartus II
Handbook.

■ Force Use of Synchronous Clear Signals—Forces the compiler to

utilize synchronous clear signals in normal mode logic cells.
Turning on this option helps to reduce the total number of logic cells
used in the design, but might negatively impact the fitting because
synchronous control signals are shared by all the logic cells in a LAB.

■ Allow Synchronous Control Signals—Allows the compiler to utilize

synchronous clear and/or synchronous load signals in normal
mode logic cells. Turning on this option helps to reduce the total
number of logic cells used in the design, but might negatively impact
the fitting because synchronous control signals are shared by all the
logic cells in a LAB.

f For more information about inference guidelines for registers and on

secondary control signal inference rules, refer to the Recommended HDL
Coding Styles chapter in volume 1 of the Quartus II Handbook.

Using the DFFEAS Primitive

The DFFEAS primitive allows you to directly instantiate a register in your
design and gives you control over which secondary signals are used. The
DFFEAS primitive instantiations are always adhered to unless the
secondary control signals that you use are not supported by the device
family architecture. If you instantiate a DFFEAS primitive with
unsupported secondary control signals, they are converted into the
equivalent logic.

1 For an example on instantiation of the DFFEAS primitive, refer

to the Primitive Reference and Synthesis Attributes chapter in this
user guide.

Creating Memory for Your Design

You can create RAM for your design in two ways. The first method
involves creating HDL code that infers a memory function. The second
method involves building a function using the MegaWizard
Manager and instantiating the resulting custom megafunction variation
file in your design.

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April 2007 Designing with Low-Level Primitives User Guide

®

Plug-In

Low-Level Primitive Examples

f For RAM inference guidelines, refer to the Recommended HDL Coding

Inferring RAM Functions from HDL Code

To infer RAM functions, synthesis tools detect sets of registers and logic
that can be replaced with the altsyncram or lpm_ram_dp megafunctions,
depending on the targeted device family. The Quartus II software usually
does not infer very small RAM blocks because they typically are
implemented more efficiently by using the registers in regular logic.

If your design contains a RAM block that your synthesis tool does not
recognize and infer, the design might require a large amount of system
memory, which can potentially cause run-time compilation problems.

Styles chapter of the Quartus II Handbook.

Using the MegaWizard Plug-In Manager

You can use the MegaWizard Plug-In Manager to create RAM functions.
The MegaWizard Plug-In Manager, located in the Tools menu in the
Quartus II software, allows you create or modify design files that contain
custom megafunction variations, which you can then instantiate in a
design file.

The GUI-based interface of the MegaWizard Plug-In Manager provides
an easy and intuitive interface that allows you to parameterize complex
functions such as memory. However, there are cases, particularly with
memory, where you simply want to modify a small component of the
megafunction. For example, your design can call for two types of memory
functions: a 32, 8-bit word single-port memory function and a 64, 8-bit
word single-port memory function. In this scenario, you can use the
MegaWizard Plug-In Manager to create one function and then use the
instantiation from the wizard-generated file to directly instantiate the
second variation. However, directly instantiating memory functions
should only be used when the modifications to the functions are minimal.

Example 1–6 shows a Verilog example for a 32, 8-bit word single-port

memory function.

1–10 Altera Corporation
Designing with Low-Level Primitives User Guide April 2007

Example 1–6. A 32, 8-Bit Word Single-Port Memory Function, Verilog

altsyncramalt syncram_component (

.wren_a (wren),
.clock0 (clock),
.address_a (wraddress),
.address_b (rdaddress),
.data_a (data_in),
.q_b (data_out),
.aclr0 (1'b0),
.aclr1 (1'b0),
.clocken1 (1'b1),
.clocken0 (1'b1),
.q_a (),
.data_b ({8{1'b1}}),
.rden_b (1'b1),
.wren_b (1'b0),
.byteena_b (1'b1),
.addressstall_a (1'b0),
.byteena_a (1'b1),
.addressstall_b (1'b0),
.clock1 (1'b1));

defparam

altsyncram_component.address_aclr_a = "NONE",

altsyncram_component.address_aclr_b = "NONE",

altsyncram_component.address_reg_b = "CLOCK0",

altsyncram_component.indata_aclr_a = "NONE",

altsyncram_component.intended_device_family = "Stratix",

altsyncram_component.lpm_type = "altsyncram",

Low-Level Primitive Design

//This is where a 32, 8-bit word is modified.

altsyncram_component.numwords_a = 32,

altsyncram_component.numwords_b = 32,

altsyncram_component.operation_mode = "DUAL_PORT",

altsyncram_component.outdata_aclr_b = "NONE",

altsyncram_component.outdata_reg_b = "CLOCK0",

altsyncram_component.power_up_uninitialized = "FALSE",

altsyncram_component.read_during_write_mode_mixed_ports =

"DONT_CARE",

altsyncram_component.widthad_a = 5,

altsyncram_component.widthad_b = 5,

//This is the width of the input port.

altsyncram_component.width_a = 8,

altsyncram_component.width_b = 8,

altsyncram_component.width_byteena_a = 1,

altsyncram_component.wrcontrol_aclr_a = "NONE";

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Low-Level Primitive Examples

Example 1–7 shows a Verilog example for a 64, 8-bit word single-port

memory function.

Example 1–7. A 64, 8-Bit Word Single-Port Memory Function, Verilog

altsyncram altsyncram_component (

.wren_a (wren),
.clock0 (clock),
.address_a (wraddress),
.address_b (rdaddress),
.data_a (data_in),
.q_b (data_out),
.aclr0 (1'b0),
.aclr1 (1'b0),
.clocken1 (1'b1),
.clocken0 (1'b1),
.q_a (),
.data_b ({8{1'b1}}),
.rden_b (1'b1),
.wren_b (1'b0),
.byteena_b (1'b1),
.addressstall_a (1'b0),
.byteena_a (1'b1),
.addressstall_b (1'b0),
.clock1 (1'b1));

defparam

altsyncram_component.address_aclr_a = "NONE",

altsyncram_component.address_aclr_b = "NONE",

altsyncram_component.address_reg_b = "CLOCK0",

altsyncram_component.indata_aclr_a = "NONE",

altsyncram_component.intended_device_family = "Stratix",

altsyncram_component.lpm_type = "altsyncram",

//This is where a 64, 8-bit word is modified.

altsyncram_component.numwords_a = 64,

altsyncram_component.numwords_b = 64,

altsyncram_component.operation_mode = "DUAL_PORT",

altsyncram_component.outdata_aclr_b = "NONE",

altsyncram_component.outdata_reg_b = "CLOCK0",

altsyncram_component.power_up_uninitialized = "FALSE",

altsyncram_component.read_during_write_mode_mixed_ports

="DONT_CARE",

altsyncram_component.widthad_a = 6,

altsyncram_component.widthad_b = 6,

//This is the width of the input port.

altsyncram_component.width_a = 8,

altsyncram_component.width_b = 8,

altsyncram_component.width_byteena_a = 1,

altsyncram_component.wrcontrol_aclr_a = "NONE";

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Designing with Low-Level Primitives User Guide April 2007

Look-Up Table Buffer Primitives

The look-up table (LUT) buffer primitives, LUT_INPUT and
LUT_OUTPUT, specify a LUT function in your design. These primitives

are single-input, single-output buffers that you use to create a LUT
directly in your design. The LUT_INPUT acts as an input to the
LUT_OUTPUT. If your design contains a LUT_OUTPUT primitive that is
not properly driven, the LUT_OUTPUT is ignored. By using LUT_INPUT
and LUT_OUTPUT, you can specify which LUT inputs are used. These
primitives are similar to the LCELL primitive; they give you control over
how the Quartus II synthesis engine breaks your design up into logic
cells. Because they give you full control of the inputs and outputs to a
logic cell, LUT_INPUT and LUT_OUTPUT primitives give you more
control over the synthesis process, but you must have more
understanding of the device architecture to use them successfully

Example 1–8 shows a primitive instantiation that creates a four-input

LUT that implements the function aw & bw ^ cw | dw.

Example 1–8. A Primitive Instantiation that Creates a Four-Input LUT

module lut_function (a,b,c,d,o);

input a,b,c,d;
output o;
wire aw,bw,cw,dw,o;

Low-Level Primitive Design

lut_input lut_in1 (a, aw) ;
lut_input lut_in2 (b, bw) ;
lut_input lut_in3 (c, cw) ;
lut_input lut_in4 (d, dw) ;
lut_output lut_o (aw & bw ^ cw | dw, o) ;

endmodule

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April 2007 Designing with Low-Level Primitives User Guide

Low-Level Primitive Examples

Example 1–9 is a more complex example using parameterized Verilog

and the LUT_INPUT and LUT_OUTPUT primitive buffers. This example
creates a LUT function to implement an arbitrary function in a single
LUT. The value of “out” is generated by the mask signal and uses the
LUT_INPUT and LUT_OUTPUT primitive buffers to build a single logic
cell that implements the functionality given by the LUT_MASK parameter.

Example 1–9. Parameterized Verilog and LUT_INPUT and LUT_OUTPUT Primitive Buffers

module lut_sub (din,out);

parameter LUT_SIZE = 4;
parameter NUM_BITS = 2**LUT_SIZE;

input [LUT_SIZE-1:0] din;
parameter [NUM_BITS-1:0] mask = {NUM_BITS{1'b0}};
output out;
wire out;

// buffer the LUT inputs
wire [LUT_SIZE-1:0] din_w;
genvar i;
generate

for (i=0; i<LUT_SIZE; i=i+1)
begin : liloop
lut_input li_buf (din[i],din_w[i]);
end

endgenerate
// build up the pterms for the LUT
wire [NUM_BITS-1:0] pterms;
generate
for (i=0; i<NUM_BITS; i=i+1)

begin : ploop
assign pterms[i] = ((din_w == i) & mask[i]);
end

endgenerate

// assign the pterms to the LUT function
wire result;
assign result = | pterms;
lut_output lo_buf (result,out);
endmodule

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Example 1–10 uses the LUT primitive to create LUTs that implement a

4-input AND and a 4-input OR function.

Example 1–10. Using the LUT Primitive

module luts (

input [3:0] in1, in2,

output out1, out2

);

lut_sub inst1 (in1, out1);
defparam inst1.mask = 16'H8000; // AND function
lut_sub inst2 (in2, out2);
defparam inst2.mask = 16'HFFFE; // OR function
endmodule

Low-Level Primitive Design

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April 2007 Designing with Low-Level Primitives User Guide

Low-Level Primitive Examples

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2. Primitive Reference

Primitives

Using primitives with HDL is an efficient way to make assignments to
your design without using the Assignment Editor.

®

The Quartus

II software supports the following primitives, described on

the corresponding pages:

■ “ALT_INBUF”

■ “ALT_OUTBUF” on page 2–3

■ “ALT_OUTBUF_TRI” on page 2–6

■ “ALT_IOBUF” on page 2–8

■ “ALT_INBUF_DIFF” on page 2–11 (1)

■ “ALT_OUTBUF_DIFF” on page 2–13 (1)

■ “ALT_OUTBUF_TRI_DIFF” on page 2–14 (1)

■ “ALT_IOBUF_DIFF” on page 2–19 (1)

■ “ALT_BIDIR_DIFF” on page 2–22 (1)

■ “ALT_BIDIR_BUF” on page 2–25 (1)

■ “LCELL” on page 2–27

■ “DFF” on page 2–28

■ “CARRY and CARRY_SUM” on page 2–29

■ “CASCADE” on page 2–30

■ “LUT_INPUT” on page 2–31

■ “LUT_OUTPUT” on page 2–32

Note to the above list:

(1) These I/O primitives are supported only in Stratix®III and Cyclone®III device

families.

ALT_INBUF

The primitive allows you to make a location assignment, termination
assignment, and also lets you determine whether to use weak pull up
resistor, whether to enable bus-hold circuitry or an io_standard
assignment to an input pin from a lower-level entity. Table 2–1 describes

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April 2007

Primitives

the input and output ports and the parameters associated with

ALT_INBUF. If any other parameter is specified (for example,
current_strength) an error will result.

Table 2–1. ALT_INBUF Ports and Parameters

Port/Parameter Description/Value

Input Ports

i

Connect this port to a chip input pin or to a wire to be connected to an input pin.
There must be no logic between the i port and the chip input pin. If there is, an
error results.

Output Ports

o

Connect this port to the logic in the design to receive the input signal.

Parameter

io_standard

location

A logic option that specifies the I/O standard of a pin. Different device families
support different I/O standards, and restrictions apply to placing pins with
different I/O standards together.

Any legal pin location for the current device.

enable_bus_hold An option to enable bus-hold circuitry. Legal values are “on” and “off.”

weak_pull_up_resistor An option to enable the weak pull-up resistor. Legal values are “on” and “off.”

termination

Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination. For GX
families, you must use Assignment Editor in the Quartus II software to set the
type of termination on high-speed transceivers.

This parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy
and Cyclone II.

®

Example 2–1 shows a Verilog HDL example of an ALT_INBUF primitive

instantiation.

Example 2–1. ALT_INBUF Primitive Instantiation, Verilog HDL

alt_inbuf my_inbuf (.i(in), .o(internal_sig));

//in must be declared as an input pin

defparam my_inbuf.io_standard = "2.5 V";
defparam my_inbuf.location = "IOBANK_2";
defparam my_inbuf.enable_bus_hold = "on";
defparam my_inbuf.weak_pull_up_resistor = "off";
defparam my_inbuf.termination = "parallel 50 ohms";

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Designing with Low-Level Primitives User Guide April 2007

II

Example 2–2 shows a VHDL component declaration for an ALT_INBUF

primitive instantiation.

Example 2–2. ALT_INBUF Primitive Component Declaration, VHDL

COMPONENT ALT_INBUF
GENERIC

(IO_STANDARD : STRING :="NONE";

WEAK_PULL_UP_RESISTOR : STRING :="NONE";

LOCATION : STRING :="NONE";

ENABLE_BUS_HOLD : STRING :="NONE";

WEAK_PULL_UP_RESISTOR : STRING :="NONE";

TERMINATION : STRING :="NONE");
PORT (i : IN STD_LOGIC;

o : OUT STD_LOGIC);

END COMPONENT;

ALT_OUTBUF

The primitive allows you to make a location assignment,
io_standard assignment, current_strength assignments,

termination assignment, and also lets you determine whether to use weak
pull-up resistor, whether to enable bus-hold circuitry and/or a
slow_slew_rate assignment to an output pin from a lower-level entity.

Primitive Reference

Table 2–2 explains the ALT_OUTBUF input and output ports, and the

parameter options. If any other parameter is specified, an error will
result.

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Primitives

Table 2–2. ALT_OUTBUF Ports & 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

Connect this port to a chip output pin or a wire to be connected to a chip output.
There must be no logic between the o port and the chip output pin. If there is,
an error results.

Parameter

io_standard A logic option that specifies the I/O standard of a pin. Different device families

support different I/O standards, and restrictions apply to placing pins with
different I/O standards together.

current_strength

location

A logic option that sets the drive strength of a pin. Specific numerical strength
settings are appropriate only for pins with certain I/O standards. You can specify
any legal current strength value here (including “minimum current” or “maximum
current”).The parameter name
for backward compatibility.

Any legal pin location for the current device.

current_strength_new is also supported

enable_bus_hold An option to enable bus-hold circuitry. Legal values are “on” and “off.”

weak_pull_up_resistor An option to enable the weak pull-up resistor. Legal values are “on” and “off.”

termination

slow_slew_rate

Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination.
This parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy II,
Cyclone III, and Cyclone II.

A logic option that implements slow low-to-high or high-to-low transitions on
output pins to help reduce switching noise. Current legal values are “
“

off.”

on” and

This assignment is ignored by the Fitter for Stratix II and Cyclone II devices.
This parameter is not supported for Stratix II GX or HardCopy II devices.

slew_rate The slow_slew_rate parameter is not available for Stratix III and

Cyclone III. These two families support the

Accepts any positive integer value, including 0. The default value is –1, which
is equivalent to not using this parameter.
This parameter is available only for Stratix III and Cyclone III.

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Designing with Low-Level Primitives User Guide April 2007

slew_rate parameter instead.

Primitive Reference

Example 2–3 shows a Verilog HDL example of an ALT_OUTBUF primitive

instantiation.

Example 2–3. ALT_OUTBUF Primitive Instantiation, Verilog HDL

alt_outbuf my_outbuf (.i(internal_sig), .o(out)); //out must be declared as
an output pin
defparam my_outbuf.io_standard = "2.5 V";
defparam my_outbuf.slow_slew_rate = "on";

defparam my_outbuf.enable_bus_hold = "off";

defparam my_outbuf.weak_pull_up_resistor = "on";
defparam my_outbuf.termination = "series 25 ohms";

Example 2–4 shows a VHDL component declaration for an ALT_OUTBUF

primitive instantiation.

Example 2–4. ALT_OUTBUF Primitive Instantiation, VHDL

COMPONENT alt_outbuf
GENERIC(

IO_STANDARD : STRING :="NONE";
CURRENT_STRENGTH : STRING :="NONE";
SLOW_SLEW_RATE : STRING :="NONE";
LOCATION : STRING :="NONE";
ENABLE_BUS_HOLD : STRING :="NONE";
WEAK_PULL_UP_RESISTOR : STRING :="NONE";
TERMINATION : STRING :="NONE";
SLEW_RATE:INTEGER := -1

);
PORT (

i : IN STD_LOGIC;
o : OUT STD_LOGIC

);
END COMPONENT;

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Primitives

ALT_OUTBUF_TRI

The primitive allows you to make a location assignment, io_standard
assignment, current_strength assignment, termination assignment,
whether or not to use weak pull-up resistor, and allows you to determine
whether or not to enable bus-hold circuitry and/or a slow_slew_rate
assignment to a tri-stated output pin from a lower-level entity. Table 2–3
explains the ALT_OUTBUF_TRI input and output ports, as well as the
parameter options. If any other parameter is specified, an error will
result.

Example 2–5 shows a Verilog HDL example of an ALT_OUTBUF_TRI

primitive instantiation.

Example 2–5. ALT_OUTBUF_TRI Primitive Instantiation, Verilog HDL

alt_outbuf_tri my_outbuf tri (.i(internal_sig), .oe(enable_sig),
.o(out));

//out must be declared as an output pin

defparam my_outbuf_tri.io_standard = “1.8 V”;
defparam my_outbuf_tri.current_strength =
"maximum current";
defparam my_outbuf_tri.slow_slew_rate = “off”;

Example 2–6 shows a VHDL component declaration for an

ALT_OUTBUF_TRI primitive instantiation.

Example 2–6. ALT_OUTBUF_TRI Primitive Component Declaration, VHDL

COMPONENT alt_outbuf_tri
GENERIC (

IO_STANDARD : STRING :="NONE";
CURRENT_STRENGTH : STRING :="NONE";
SLOW_SLEW_RATE : STRING :="NONE";
LOCATION : STRING :="NONE";
ENABLE_BUS_HOLD : STRING :="NONE";
WEAK_PULL_UP_RESISTOR : STRING :="NONE";
TERMINATION : STRING :="NONE";
SLEW_RATE:INTEGER := -1

);
PORT (

i : IN STD_LOGIC;
oe : IN STD_LOGIC;
o : OUT STD_LOGIC

);

END COMPONENT;

2–6 Altera Corporation
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Primitive Reference

Table 2–3. ALT_OUTBUF_TRI Ports & Parameters

Port/Parameter Description/Value

Input Ports

i

oe

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

Connect this port to the tristate output enable logic.

Output Ports

o

Connect this port to a chip output pin or a wire to be connected to a chip output.
There must be no logic between the
an error results.

o port and the chip output pin. If there is,

Parameters

io_standard

current_strength

location

A logic option that specifies the I/O standard of a pin. Different device families
support different I/O standards, and restrictions apply to placing pins with
different I/O standards together.

A logic option that sets the drive strength of a pin. Specific numerical strength
settings are appropriate only for pins with certain I/O standards. You can
specify any legal current strength value here (including “minimum current” or
“maximum current”). The parameter name
also supported for backward compatibility.

The location is any legal pin location for the current device.

current_strength_new is

enable_bus_hold An option to enable bus-hold circuitry. Legal values are “on” and “off.”

weak_pull_up_resistor An option to enable the weak pull-up resistor. Legal values are “on” and “off.”

termination

slow_slew_rate

Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination.
This parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy II,
Cyclone III, and Cyclone II.

A logic option that implements slow low-to-high or high-to-low transitions on
output pins to help reduce switching noise. Current legal values are “

off.”

“

on” and

This assignment is ignored by the Fitter for Stratix II and Cyclone II devices.
This parameter is not supported for Stratix II GX or HardCopy II devices.

slew_rate The slow_slew_rate parameter is not available for Stratix III and

Cyclone III. These two families support the

Accepts any positive integer value including 0. Default value is –1, which is
equivalent to not using this parameter. Available only for Stratix III and
Cyclone III.

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slew_rate parameter instead.

Primitives

ALT_IOBUF

The primitive allows you to make a location assignment,
io_standard assignment, current_strength assignment,

termination assignment, and allows you to determine whether or not to
use weak pull-up resistor, whether or not to enable bus-hold circuitry
and/or a slow_slew_rate assignment to a bidirectional pin from a
lower-level entity.

Table 2–4 lists the ports and parameters of the ALT_IOBUF primitive, and

their respective descriptions and possible values.

Example 2–7 shows a Verilog HDL example of an ALT_IOBUF primitive

instantiation.

Example 2–7. ALT_IOBUF Primitive Instantiation, Verilog HDL

alt_iobuf my_iobuf (.i(internal_sig1), .oe(enable_sig),
.o(internal_sig2), .io(bidir));
//bidir must be declared as an inout pin
defparam my_iobuf.io_standard = "3.3-V PCI";
defparam my_iobuf.current_strength = "minimum current";
defparam my_iobuf.slow_slew_rate = "on";
defparam my_iobuf.location = "iobank_1";

Example 2–8 shows a VHDL component declaration for an ALT_IOBUF

primitive instantiation.

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Primitive Reference

Table 2–4. ALT_IOBUF Ports and Parameters

Port/Parameter Description/Value

Input Ports

i

oe

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

o

Bidirectional Port

Connect this port to the logic in the design that receives the input signal

Connect this port to the chip bidir pin or an entity bidir port. There must
be no logic between the
results.

io port and the chip bidir pin. If there is, an error

Parameter

io_standard

current_strength

location

A logic option that specifies the I/O standard of a pin. Different device families
support different I/O standards, and restrictions apply to placing pins with
different I/O standards together.

A logic option that sets the drive strength of a pin. Specific numerical strength
settings are appropriate only for pins with certain I/O standards. You can
specify any legal current strength value here (including “minimum current” or
“maximum current”). The parameter name
supported for backward compatibility.

Any legal pin location for the current device.

current_strength_new is also

enable_bus_hold An option to enable bus-hold circuitry. Legal values are “on” and “off.”

weak_pull_up_resistor An option to enable the weak pull-up resistor. Legal values are “on” and “off.”

termination

Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination.
This parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy II,
Cyclone III, and Cyclone II.

To set separate input and output values, use

input_termination and

output_termination parameters instead. This parameter can not be

used along with

This parameter sets both input termination value and output termination values
for Stratix III and Cyclone III devices. However, note that the Fitter ignores any
input termination parameters for Cyclone III devices.

To set separate input and output values, use

input_termination or output_termination.

input_termination and

output_termination parameters instead. This parameter can not be

used with

input_termination

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April 2007 Designing with Low-Level Primitives User Guide

Any legal input on-chip termination value for the current device. This parameter
cannot be used with the
supported in Stratix III devices only.

input_termination or output_termination.

termination parameter. This parameter is

Primitives

Table 2–4. ALT_IOBUF Ports and Parameters

Port/Parameter Description/Value

output_termination

slow_slew_rate

slew_rate The slow_slew_rate parameter is not available for Stratix III and

Any legal output on-chip termination value for the current device. This
parameter cannot be used with the termination parameter. this parameter is
supported in Stratix III and Cyclone III devices.

A logic option that implements slow low-to-high or high-to-low transitions on
output pins to help reduce switching noise. Current legal values are “

off.”

“

This assignment is ignored by the Fitter for Stratix II and Cyclone II devices.
This parameter is not supported for Stratix II GX or HardCopy II devices.

Cyclone III. These two families support the

Accepts any positive integer value including 0. Default value is –1, which is
equivalent to not using this parameter. Available only for Stratix III and
Cyclone III.

slew_rate parameter instead.

Example 2–8. ALT_IOBUF Primitive Component Declaration, VHDL

COMPONENT alt_iobuf
GENERIC (

IO_STANDARD : STRING :="NONE";
CURRENT_STRENGTH : STRING :="NONE";
SLOW_SLEW_RATE : STRING :="NONE";
LOCATION : STRING :="NONE";
ENABLE_BUS_HOLD : STRING :="NONE";
WEAK_PULL_UP_RESISTOR : STRING :="NONE";
TERMINATION : STRING :="NONE";
INPUT_TERMINATION : STRING := "NONE" ;
OUTPUT_TERMINATION : STRING := "NONE";
SLEW_RATE:INTEGER := -1

);
PORT (

i : IN STD_LOGIC;
oe: IN STD_LOGIC;
io : INOUT STD_LOGIC;
o : OUT STD_LOGIC );

on” and

END COMPONENT;

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Primitive Reference

ALT_INBUF_DIFF

This primitive allows you to name and connect positive and negative pins
when a differential I/O standard is used for an input pin. You can assign
I/O standard assignments, location assignments, termination
assignments, control bus hold circuitry, and enable weak pull up on the
input pins. An attempt to set any other parameter will result in an error.

Table 2–5 lists the ports and parameters of the ALT_INBUF_DIFF

primitive, and their respective descriptions and possible values.

Table 2–5. ALT_INBUF_DIFF Ports and Parameters

Port/Parameter Description/Value

Input Ports

i

ibar

Output Ports

o Connect this port to the logic in the design to receive the input signal.

Parameter Name

io_standard

location

enable_bus_hold An option to enable bus-hold circuitry. Legal values are “on” and “off.”

weak_pull_up_resistor An option to enable the weak pull-up resistor. Current legal values are “on” and

termination

This port represents the positive pin of a differential I/O standard.
Connect this port either to the device’s input pin or to a wire to be connected to
an input pin. There must be no logic between the
pin. The input pin cannot have any other fan-out.

This port represents the negative pin of a differential I/O standard.
Connect this port either to the device's input pin or to a wire to be connected to
an input pin. There must be no logic between the
pin. The input pin cannot have any other fan-out.

Any legal differential I/O standard value.

Any legal pin location for the current device.

off”.

“

Any legal on-chip-termination value for the current device. For GX families, this
parameter supports only regular termination, and not GXB termination. This
parameter is supported for Stratix III, Stratix II, Stratix II GX, HardCopy II, and
Cyclone II.

i port and the device's input

ibar port and the chip input

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

Each parameter also accepts the value “none”. Assigning the value
“none” to any parameter is equivalent to not setting the parameter. Note
that the primitive requires that all three ports (i, ibar, and o) are
connected. Also note that all parameters are optional.

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Primitives

Example 2–9 shows a VHDL component instantiation example of an

ALT_INBUF_DIFF primitive.

Example 2–9. ALT_INBUF_DIFF Primitive, VHDL Component Instantiation

library ieee;
use ieee.std_logic_1164.all;
library altera;
use altera.altera_primitives_components.all;

entity test_inbuf is
port (

in1,in2,in3 : in std_logic;
out1 : out std_logic

);
end test_inbuf;

architecture test of test_inbuf is

signal tmp1: std_logic;

begin

inst : ALT_INBUF_DIFF
generic map (

IO_STANDARD => "LVDS",7
LOCATION => "IOBANK_3"

)
port map (

i => in1,
ibar => in2,
o => tmp1

) ;

out1 <= in3 and tmp1;

end test;

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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.

Table 2–6. ALT_OUTBUF_DIFF Ports and Parameters

Port/Parameter Description/Value

Input Ports

i

Output Ports

o

obar

Parameter Name

io_standard

current_strength Any legal value of the current_strength_new QSF assignment.

location

slew_rate

enable_bus_hold Whether or not to enable bus-hold circuitry. Current legal values are “on” and

weak_pull_up_resistor Whether or not to enable the weak pull-up resistor. Current legal values are “on”

termination

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

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
pin. This port cannot have multiple fan-outs.

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
output pin. This port cannot have multiple fan-outs.

Any legal differential I/O standard value.

Any legal pin location for the current device.

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

off”.

“

off”.

and “

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

0).

o port and the chip output

obar port and the chip

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

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Primitives

the default. Assigning –1 to slew_rate is equivalent to not setting the
parameter. Note that the primitive requires that all three ports (i, o, and
obar) are connected. Also note that all parameters are optional.

Example 2–10 shows a VHDL component instantiation example of an

ALT_OUTBUF_DIFF primitive.

Example 2–10. ALT_OUTBUF_DIFF Primitive, VHDL Component Instantiation

library ieee;
use ieee.std_logic_1164.all;
library altera;
use altera.altera_primitives_components.all;

entity test_outbuf is
port (

in1, in2 : in std_logic;
out1, out1_n : out std_logic

);
end test_outbuf;

architecture test of test_outbuf is

signal tmp: std_logic;

begin
inst : ALT_OUTBUF_DIFF
generic map (

IO_STANDARD => "LVDS",

LOCATION=> "IOBANK_3"
)
port map (

i => tmp,

o => out1,

obar => out1_ n

) ;

tmp <= in1 and in2;

end test;

ALT_OUTBUF_TRI_DIFF

This primitive allows you to name and connect positive and negative pins
when a differential I/O standard is used for a tri-statable 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.

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Primitive Reference

Table 2–7 lists the ports and parameters of the ALT_OUTBUF_TRI_DIFF

primitive, and their respective description and possible values.

Table 2–7. ALT_OUTBUF_TRI_DIFF Ports and Parameters

Port/Parameter Description/Value

Input Ports

i

oe

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

o

obar

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
pin. This port cannot have multiple fan-outs.

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
output pin. This port cannot have multiple fan-outs.

o port and the chip output

obar port and the chip

Parameter Name

io_standard

Any legal differential I/O standard value.

current_strength Any legal value of the current_strength_new QSF assignment.

location

slew_rate

Any legal pin location for the current device.

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

termination

Whether or not to enable the weak pull-up resistor. Current legal values are

on” and “off”.

“

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

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.

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April 2007 Designing with Low-Level Primitives User Guide

Primitives

Example 2–11. ALT_OUTBUF_TRI_DIFF Primitive Instantiation, Verilog HDL

module test (

datain_h,
datain_l,
oe,
outclock,
dataout,
dataout_n

);

input datain_h;
input datain_l;
input outclock;
input oe;
output dataout;
output dataout_n;

wire tmp_out;
wire tmp_oe;

my_altddio_out altddio_out_inst (

.outclock (outclock),

.datain_h (datain_h),

.datain_l (datain_l),

.dataout (tmp_out),

.aclr (1'b0),

.aset (1'b0),

.oe (oe),

.outclocken (1'b1),

.oe_out (tmp_oe),

.sclr (1'b0)

);

ALT_OUTBUF_TRI_DIFF my_outbuf (

.i (tmp_out),
.oe (tmp_oe),
.o(dataout),
.obar(dataout_n)
);

defparam my_outbuf.io_standard = "LVDS";

endmodule

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Example 2–12. ALT_OUTBUF_TRI_DIFF Primitive, VHDL Component Instantiation

library ieee;
use ieee.std_logic_1164.all;
library altera;
use altera.altera_primitives_components.all;
entity test_outbuf_tri is
port (

datain_h, datain_l : in std_logic_vector (0 downto 0);

oe, outclock : in std_logic;

dataout, dataout_n : out std_logic

);
end test_outbuf_tri;

architecture test of test_outbuf_tri is

component altddio_out
generic (

intended_device_family: STRING;
lpm_type : STRING;
power_up_high : STRING;
width : NATURAL

);
port (

dataout : OUT STD_LOGIC_VECTOR (0 DOWNTO 0);
outclock : IN STD_LOGIC ;
oe : IN STD_LOGIC ;
datain_h : IN STD_LOGIC_VECTOR (0 DOWNTO 0);
datain_l : IN STD_LOGIC_VECTOR (0 DOWNTO 0)

);
end component;

Primitive Reference

signal tmp_out : std_logic_vector (0 downto 0);
signal tmp_oe : std_logic;

begin

DDIO_OUT : altddio_out
generic map (

intended_device_family => "Stratix II",
lpm_type => "altddio_out",
power_up_high => "OFF",
width => 1

)
port map (

outclock => outclock,
oe => tmp_oe,
datain_h => datain_h,
datain_l => datain_l,
dataout => tmp_out

);

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Primitives

inst : ALT_OUTBUF_TRI_DIFF
generic map (

IO_STANDARD => "LVDS",

LOCATION=> "IOBANK_3"
)
port map (

i => tmp_out,

oe => tmp_oe,

o => dataout,

obar => dataout_n

) ;

end test;

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ALT_IOBUF_DIFF

This primitive allows you to name and connect positive and negative pins
when a differential I/O standard is used for a bidirectional pin. You can
assign I/O standard, location, drive strength (current strength), slew rate,
and termination assignments, enable bus hold circuitry, and enable weak
pull-up resistor on the bidir pins. An attempt to set any other parameter
will result in an error.

Table 2–8 lists the ports and parameters of the ALT_IOBUF_DIFF

primitive, and their respective descriptions and possible values.

Table 2–8. ALT_IOBUF_DIFF Ports and Parameters (Part 1 of 2)

Port/Parameter Description/Value

Input Port

i

oe

Output Ports

o

Bidirectional Port

io

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

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

Connect this port to the logic in the design that receives the input signal.

This port represents the positive pin of a differential I/O standard.

Primitive Reference

bidir pin or an entity bidir port. There

io port and the chip bidir port.

bidir pin, or an entity bidir port. There

iobar port and the chip bidir port.

iobar

Connect this port to the device’s
must be no logic between the

This port represents the negative pin of a differential I/O standard.

Connect this port to the device’s
must be no logic between the

Parameter Name

io_standard

current_strength Any legal value of the current_strength_new QSF assignment.

location

slew_rate

enable_bus_hold The ability to enable bus-hold circuitry. Current legal values are “on” and “off”.

weak_pull_up_resistor The ability to enable the weak pull-up resistor. Current legal values are “on” and

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April 2007 Designing with Low-Level Primitives User Guide

Any legal differential I/O standard value.

Any legal pin location for the current device.

Any legal slew rate value for the current device. This value must be a positive
integer (including 0).

off”.

“

Primitives

Table 2–8. ALT_IOBUF_DIFF Ports and Parameters (Part 2 of 2)

Port/Parameter Description/Value

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

output_termination parameters instead.

input_termination and

input_termination

output_termination

This parameter cannot be used with

output_termination.

Any legal input on-chip-termination value for the current device. This parameter
cannot be used with the
Note: The Fitter ignores this parameter for Cyclone III devices.

Any legal output on-chip-termination value for the current device. This
parameter cannot be used with the

termination parameter.

input_termination or

termination parameter.

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 five ports (i, oe, o, io,
and iobar) are connected. Also note that all parameters are optional.

Example 2–13 shows an example of a VHDL component instantiation,

and Example 2–14 shows a Verilog HDL example of an
ALT_IOBUF_DIFF primitive instantiation.

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Example 2–13. ALT_IOBUF_DIFF Primitive, VHDL Component Instantiation

library ieee;
use ieee.std_logic_1164.all;
library altera;
use altera.altera_primitives_components.all;
entity test_iobuf is
port (

in1, in2, oe : in std_logic;
bidir, bidir_n : inout std_logic;
out : out std_logic

);
end test_iobuf;

architecture test of test_iobuf is

signal tmp1: std_logic;

tmp1 <= in1 and in2;

begin

inst : ALT_IOBUF_DIFF
generic map (

IO_STANDARD => "LVDS",

LOCATION=> "IOBANK_3"
)
port map (

i => tmp1,

oe => oe,

o => out,

io => bidir,

iobar => bidir_n

) ;

Primitive Reference

end test;

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Primitives

Example 2–14. ALT_IOBUF_DIFF Primitive Instantiation, Verilog HDL

module test(in1,in2,oe,out,bidir,bidir_n);
input in1;
input in2;
input oe;
inout bidir;
inout bidir_n;
output out;
wire tmp1;
and(tmp1,in1,in2);

ALT_IOBUF_DIFF inst(.i(tmp1), .oe(oe), .o(out), .io(bidir),
.iobar(bidir_n));
defparam inst.io_standard = "LVDS";
defparam inst.current_strength = "12mA";
endmodule

ALT_BIDIR_DIFF

This primitive allows you to name and connect positive and negative pins
when the altddio_bidir megafunction is used your design. 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 bidir pins. An attempt to set any other parameter
will result in an error.

Table 2–9 lists the ports and parameters of the ALT_BIDIR_DIFF

primitive, and their respective description and possible values.

Table 2–9. ALT_BIDIR_DIFF Ports and Parameters (Part 1 of 2)

Port/Parameter Description/Value

Input Ports

oe Connect this port to the oe_out port of the altddio_bidir megafunction.

Bidirectional Port

bidirin Connect this port to the padio port of the altddio_bidir megafunction. The

padio port should not have any other fan-outs.

io

iobar

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This port represents the positive pin of a differential I/O standard.
Connect this port to the device’s
must be no logic between the

This port represents the negative pin of a differential I/O standard.
Connect this port to the device's
must be no logic between the

bidir pin or an entity bidir port. There

io port and the chip bidir port.

bidir pin or an entity bidir port. There

iobar port and the chip bidir port.

Primitive Reference

Table 2–9. ALT_BIDIR_DIFF Ports and Parameters (Part 2 of 2)

Port/Parameter Description/Value

Parameter Name

io_standard

Any legal differential I/O standard value.

current_strength Any legal value of the current_strength_new QSF assignment.

location

slew_rate

Any legal pin location for the current device.

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”

off”.

and “

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.

input_termination

output_termination

This parameter cannot be used along with

input_termination or

output_termination.

Any legal input on-chip-termination value for the current device. This parameter
can not be used along with the “

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

Any legal output on-chip-termination value for the current device. This
parameter can not be used along with the “

termination” parameter.

termination” parameter.

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 (oe,
bidirin, io, and iobar) are connected. Also note that all parameters
are optional. This primitive can only be used with an altddio_bidir
megafunction, and with the port connections described above; using it in
any other configuration will result in an error.

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Primitives

Example 2–15 shows an example of a Verilog HDL primitive

instantiation, and Example 2–16 shows a VHDL example of an
ALT_BIDIR_DIFF component declaration.

Example 2–15. ALT_BIDIR_DIFF Primitive Instantiation, Verilog HDL

module ddio_top (aset, combout, datain_h, datain_l, inclock, sclr, oe,
outclock, bidir, bidir_n );
input aset;
input sclr;
input datain_h;
input datain_l;
input inclock;
input oe;
input outclock;
output combout;
inout bidir;
inout bidir_n;
wire tmp_oe;
wire tmp_padio;

//myddio_bidir is an instance of the altddio_bidir megafunction
myddio_bidir sample_ddio ( .aset(aset),
.combout(combout),
.datain_h (datain_h),
.datain_l(datain_l),
.inclock(inclock),
.oe(oe),
.outclock(outclock),
.padio(tmp_padio),
.oe_out_port(tmp_oe),
.sclr(sclr)
);

ALT_BIDIR_DIFF my_bidir (.bidirin (tmp_padio), .oe (tmp_oe), .io (bidir),
.iobar (bidir_n));
endmodule

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Example 2–16. ALT_BIDIR_DIFF Primitive, VHDL Component Declaration

component ALT_BIDIR_DIFF
generic (

IO_STANDARD : STRING := "none";
LOCATION : STRING := "none";
ENABLE_BUS_HOLD : STRING := "none";
WEAK_PULL_UP_RESISTOR : STRING := "none";
INPUT_TERMINATION : STRING := "none";
OUTPUT_TERMINATION : STRING := "none" ;
TERMINATION : STRING := "none"

);
port (

bidirin : inout std_logic;
oe: in std_logic;
io : inout std_logic;
iobar : inout std_logic

);
end component;

ALT_BIDIR_BUF

This primitive allows you to create a location assignment, io_standard
assignment, drive strength (current strength) assignment and/or
slew_rate assignment to the bidirectional pin connected to an
altddio_bidir megafunction. The legal configuration of the primitive and
the complete list of supported parameters are described in Table 2–10. If
the primitive is used in any other configuration or with any other
parameter, an error will be given.

Primitive Reference

Table 2–10. ALT_BIDIR_BUF Ports and Parameters (Part 1 of 2)

Port/Parameter Description/Value

Input Port

oe Connect this port to the oe_out port of the altddio_bidir megafunction.

Bidirectional Port

bidirin Connect this port to the padio port of the altddio_bidir megafunction. The

padio port should not have any other fan-outs.

io Connect this port to the device’s bidir pin or an entity bidir port. There

must be no logic between the

io port and the chip bidir port.

Parameter Name

io_standard

current_strength Any legal value of the current_strength_new QSF assignment.

location

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Any legal I/O standard value.

Any legal pin location for the current device.

Primitives

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

Port/Parameter Description/Value

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”

off”.

and “

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.

input_termination

output_termination

This parameter cannot be used with

input_termination or

output_termination.

Any legal input on-chip-termination value for the current device. This parameter
cannot be used along with the “

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

Any legal output on-chip-termination value for the current device. This
parameter cannot be used along with the “

termination” parameter.

termination” parameter.

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.

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Example 2–17. ALT_BIDIR_BUF Primitive, VHDL Component Declaration

component ALT_BIDIR_BUF
generic (

IO_STANDARD : STRING := "none";
LOCATION : STRING := "none";
ENABLE_BUS_HOLD : STRING := "none";
WEAK_PULL_UP_RESISTOR : STRING := "none";
SLEW_RATE : STRING := "none";
CURRENT_STRENGTH : STRING := "none";
INPUT_TERMINATION : STRING := "none";
OUTPUT_TERMINATION : STRING := "none";
TERMINATION : STRING := "none"

);
port (

bidirin : inout std_logic;
oe: in std_logic;
io : inout std_logic;

);
end component;

LCELL

The instantiation of an LCELL primitive buffer allocates one logic cell for
your design. When you instantiate an LCELL buffer in your design, the
Quartus II software preserves the assignment and does not remove it
during the synthesis process. The name that you assign the LCELL is also
preserved.

Primitive Reference

You should not use

LCELL primitives to create an intentional delay or

asynchronous pulse in your design. The delay of these elements varies
with temperature, power supply voltage, and device fabrication process.
Race conditions may occur that result in an unreliable circuit.

When you turn on the Implement as Output of Logic Cell option, or use
the synthesis attribute KEEP, an LCELL buffer is automatically inserted
by the Quartus II synthesis engine into your design.

Example 2–18 shows a Verilog HDL example of an LCELL primitive

instantiation.

Example 2–18. LCELL Primitive Instantiation, Verilog HDL

lcell <instance_name> (.in(<input_wire>), .out(<output_wire>);

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Primitives

Example 2–19 shows a VHDL component declaration for an LCELL

primitive instantiation.

Example 2–19. LCELL Primitive Instantiation, VHDL Component Declaration

COMPONENT LCELL
PORT (a_in : IN STD_LOGIC;

a_out : OUT STD_LOGIC);

END COMPONENT;

DFF

The registers in an Altera FPGA support an assortment of configurations,
and you have the option of instantiating the following configurations:

■ A DFFE (data flipflop with enable) primitive

■ A DFFEA (data flipflop with enable and asynchronous load)

primitive with additional ALOAD asynchronous load and ADATA
data signals

■ A DFFEAS (data flipflop with enable and both synchronous and

asynchronous load)

Example 2–20 shows a a Verilog HDL example of a DFF primitive

instantiation.

Example 2–20. DFF Primitive Instantiation, Verilog HDL

dffeas <instance_name> (.d(<input_wire>), .clk(<input_wire>),
.clrn(<input_wire>), .prn(<input_wire>), .ena(<input_wire>),
.asdata(<input_wire>), .aload(<input_wire>), .sclr(<input_wire>),
.sload(<input_wire>), .q(<output_wire>);

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Example 2–21 shows a VHDL component declaration for a DFF primitive

instantiation.

Example 2–21. DFF Primitive Instantiation, VHDL

COMPONENT DFFEAS
PORT (d : IN STD_LOGIC;
clk : IN STD_LOGIC;
clrn : IN STD_LOGIC;
prn : IN STD_LOGIC;
ena : IN STD_LOGIC;
asdata : IN STD_LOGIC;
aload : IN STD_LOGIC;
sclr : IN STD_LOGIC;
sload : IN STD_LOGIC;
q : OUT STD_LOGIC );
END COMPONENT;

CARRY and CARRY_SUM

The CARRY_SUM primitive is a two-input, two-output primitive that
designates the carry-out and sum-out logic for a function. The cout port
of the primitive acts as the carry-in for the next element of the carry chain.
This CARRY function also implements fast carry-chain logic for functions
such as adders and counters. The CARRY_SUM primitive does not
generate the carry or sum logic, but indicates to the compiler that the
wires connected to it should be placed on the fast carry-chain logic wires
if possible.

Primitive Reference

When you use a CARRY_SUM primitive, you must observe the following
rules:

■ The cout port of the CARRY_SUM primitive can feed one or two

cones of logic. If the CARRY_SUM primitive feeds two cones of logic,
one and only one of the cones of logic must be buffered by another
CARRY_SUM primitive. In this case, both cones of logic are
implemented in the same logic cell. You must follow this rule to tie
down the sum and carry-out functions for the first stage of an adder
or counter.

■ A cone of logic that feeds the cin port of a CARRY_SUM primitive can

have up to two inputs. A third input is allowed only if it is a
CARRY_SUM input or a q feedback from the register.

■ The cout port of the CARRY_SUM primitive cannot feed an output

pin.

■ The cin port of the CARRY_SUM primitive cannot be fed by an input

pin.

■ The cout port of two different CARRY_SUM primitives cannot feed

the same gate.

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Primitives

The CARRY primitive is supported for backward-compatibility with old
designs; new designs should use the CARRY_SUM primitive. If you use
either primitive incorrectly, it is ignored, and the Quartus II software
issues a warning message in the Message processor.

Example 2–22 shows a Verilog HDL example of a CARRY_SUM primitive

instantiation.

Example 2–22. CARRY_SUM Primitive Instantiation, Verilog HDL

carry_sum <instance_name> (.sin(<input_wire1>), .cin(<input_wire2>),
.sout(<output_wire1>), .cout(<output_wire2>);

Example 2–23 shows a VHDL component declaration for a CARRY_SUM

primitive instantiation.

Example 2–23. CARRY_SUM Primitive Instantiation, VHDL Component Declaration

COMPONENT CARRY_SUM
PORT (sin, cin : IN STD_LOGIC;
sout, cout : OUT STD_LOGIC);
END COMPONENT;

CASCADE

The CASCADE buffer enables the cascade-out function from one logic cell
and acts as a cascade-in to another logic cell. The cascade-in function
allows a cascade, which is a fast output located on each combinational
logic cell, to be OR’d or AND’d with the output of an adjacent
combinational logic cell within the FPGA.

®

The CASCADE primitive is only supported with the FLEX 10K
APEX™ family of FPGAs. If you attempt to use the CASCADE primitive
with a non-supported FPGA family, an error message occurs.

When you use a CASCADE primitive, you must observe the following
rules:

■ A CASCADE primitive can feed or be fed only by a single gate, which

must be an AND or an OR gate.

■ An inverted OR gate is treated as an AND gate and vice-versa.

Logical equivalents of AND gates are BAND, BNAND, and NOR.
Logical equivalents of OR gates are BOR, BNOR, and NAND.

■ Tw o CASCADE primitives cannot feed the same gate.

■ A CASCADE primitive cannot feed an XOR gate.

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and

■ A CASCADE primitive cannot feed an OUTPUT pin primitive or a

register.

■ The De Morgan’s inversion theorem implementation of cascaded

AND and OR gates requires all primitives in a cascaded chain to be
of the same type. A cascaded-AND gate cannot feed a cascaded-OR
gate, and vice-versa.

■ If you use the CASCADE primitive incorrectly, it is ignored and the

compiler issues a warning.

■ When you turn on the Auto Cascade Chains logic option, the

compiler automatically inserts CASCADE primitives during logic
synthesis. When you turn on the Ignore CASCADE Buffers logic
option, the compiler converts all CASCADE buffers to wire
primitives.

Example 2–24 shows a Verilog HDL example of a CASCADE primitive

instantiation.

Example 2–24. CASCADE Primitive Instantiation, Verilog HDL

cascade <instance_name> (.in(<input_wire>), .out(<output_wire>);

Example 2–25 shows a VHDL component declaration for a CASCADE

primitive instantiation.

Primitive Reference

Example 2–25. CASCADE Primitive Instantiation, VHDL Component Declaration

COMPONENT CASCADE
PORT (a_in : IN STD_LOGIC;

a_out : OUT STD_LOGIC);

END COMPONENT;

LUT_INPUT

The LUT_INPUT buffer specifies the creation of a LUT function. The
LUT_INPUT buffer marks input signals for a LUT_INPUT. The logical

functionality of the LUT_INPUT and LUT_OUTPUT buffers is a simple
wire, but together they identify LUT boundaries.

To make a LUT, you must use both input and output buffers that bound
a cone of logic.

Example 2–26 shows a Verilog HDL example of a LUT_INPUT primitive

instantiation.

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Primitives

Example 2–26. LUT_INPUT Primitive Instantiation, Verilog HDL

lut_input <instance_name> (.in(<input_wire1), .out(<output_wire>)

Example 2–27 shows a VHDL component declaration for a LUT_INPUT

primitive instantiation.

Example 2–27. LUT_INPUT Primitive Instantiation, VHDL Component Declaration

COMPONENT LUT_INPUT

PORT (a_in : IN STD_LOGIC;

a_out: OUT STD_LOGIC);

END COMPONENT;

LUT_OUTPUT

The LUT_OUTPUT buffer specifies a LUT function. The LUT_OUTPUT
buffer works like an LCELL buffer with the additional detail of specifying
the inputs and without the requirement that the LUT function has
become a hard output. The LUT_INPUT buffer is the input for a

LUT_OUTPUT buffer. The logical functionality of the LUT_OUTPUT and
LUT_INPUT buffers is a simple wire, but together they identify LUT

boundaries.

Example 2–28 shows a Verilog HDL example of a LUT_OUTPUT primitive

instantiation.

Example 2–28. LUT_OUTPUT Primitive Instantiation, Verilog HDL

lut_output <instance_name> (.in(<input_wire>), .out(<output_wire>)

Example 2–29 shows a VHDL component declaration for a LUT_OUTPUT

primitive instantiation.

Example 2–29. LUT_OUTPUT Primitive Instantiation, VHDL Component Declaration

COMPONENT LUT_OUTPUT
PORT (a_in : IN STD_LOGIC;
a_out : OUT STD_LOGIC);
END COMPONENT;

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Primitive Reference

Synthesis Attributes

Using synthesis attributes in HDL is an easy way to make assignments to
your design instead of using the Assignment Editor. Synthesis attributes
are also commonly called “pragmas”.

f For more information, refer to the Quartus II Integrated Synthesis chapter

in volume 1 of the Quartus II Handbook.

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Synthesis Attributes

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