Block Preview

Introduction

The Pattern Generator block produces digital output signals based on data loaded from a user-defined file. The ROM content is read sequentially and output at a configurable rate, making it suitable for generating arbitrary waveforms, test patterns, or stimulus signals.

The data file can be loaded directly through the Rom Content property, which opens a file dialog to select a text file containing the pattern data.

Pin Description

LEN Input integer bit INT
Number of samples to output per trigger (integer). Generation stops after LEN samples (or loops if Auto Start enabled). Default: Number of lines in the loaded data file.
Default: Must be connected
PRESCALER Input integer bit INT

Clock divider value (integer). Output rate = CLK / (PRESCALER + 1).

  • 0: Output at full clock rate
  • N: Output every N+1 clock cycles Default: 0.
Default: Must be connected
CLK Input 1 bit BIT
System clock input. All operations are synchronous to this clock. Default: Board acquisition clock.
Default: Default Board Clock
RESET Input 1 bit BIT
Synchronous reset input. Resets the ROM address counter to zero. Default: Global reset.
Default: Default Board Reset
OUT Output 1-1024 bit BIT VECTOR
Pattern data output. Width configured by the Bit Width property (1 to 1024 bits).
START 1 bit
Trigger to start pattern generation. Rising edge initiates one pattern output sequence. Only visible when Auto Start is disabled. Default: 1 (always running when Auto Start enabled).

Properties

Property window

Memory Size MemorySize

Set the amount of memory in number of words

Number of words in the ROM. Available values: 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32756, 65536, default 1024.

Default: 1024

Options: 4 8 16 32 64 128 256 512 1024 2048 4096 8192 16384 32756 65536

Bit Width BusWidth

Set the size in bits of the data

Size of each data word in bits. Range: 1 to 1024, default 16.

Default: 16

Range: 1 – 1024

Data Format Format

Select data format as Decimal or Hexadecimal

Data format for interpreting the input file.

  • HEX: Hexadecimal numbers without 0x prefix
  • SIGNED DECIMAL: Signed decimal integers
  • DECIMAL: Unsigned decimal integers Default: HEX.

Default: HEX

Options: HEX SIGNED DECIMAL DECIMAL

Auto Start Autostart

Check this option to configure the pattern generator to automatic start the generation and loop forever

Enable automatic start and continuous looping. When enabled, the START pin is hidden and generation loops forever. Default: True.

Default: True

RomContent RomContent
Content of the ROM loaded from a text file. Click to open a file dialog and select a .txt or .csv file. Each line (or comma/semicolon separated value) represents one memory address. Format must match the Data Format property setting.

Usage

Operation

The Pattern Generator reads data from an internal ROM and outputs it sequentially:

  1. On each clock cycle (divided by PRESCALER), the next ROM address is read
  2. The data at that address is output on the OUT port
  3. When LEN samples have been output, generation stops (or loops if Auto Start is enabled)

Data File Format

The Rom Content property allows loading a text file containing the pattern data. The file format depends on the Data Format property setting:

HEX Format

Each line contains a hexadecimal number without the 0x prefix:

  A012
12
133
F0F1
FFFF
0000

SIGNED DECIMAL Format

Each line contains a signed decimal integer:

  -32768
-100
0
100
32767

DECIMAL (Unsigned) Format

Each line contains an unsigned decimal integer:

  0
100
255
1000
65535

File Parsing Rules

When loading a file, the following separators are automatically converted to newlines:

  • Comma (,)
  • Semicolon (;)
  • Space ( )
  • Tab

This allows flexible input formats like CSV files:

  A012, 12, 133, F0F1

is equivalent to:

  A012
12
133
F0F1

Memory Configuration

Property Description
Memory Size Number of words in ROM (4 to 65536)
Bit Width Size of each word in bits (1 to 1024)

Important: If the data file contains fewer lines than Memory Size, the remaining addresses are filled with zeros.

Data Format Property

The Data Format property determines how numbers in the file are interpreted:

Format Description Example Values
HEX Hexadecimal without 0x prefix FF, A012, 1234
SIGNED DECIMAL Signed integer -128, 0, 127
DECIMAL Unsigned integer 0, 128, 255

Note for Xilinx FPGAs: The internal .mem file always uses hexadecimal format. If SIGNED DECIMAL or DECIMAL is selected, values are automatically converted to hexadecimal during compilation.

Output Timing

The output sample rate is controlled by the PRESCALER input:

$$ f_{out} = \frac{f_{clk}}{\text{PRESCALER} + 1} $$

where $f_{clk}$ is the frequency of the CLK input.

PRESCALER Clock Division Output Rate @ 100 MHz
0 1 100 MHz
1 2 50 MHz
9 10 10 MHz
99 100 1 MHz

Auto Start Mode

When Auto Start is enabled:

  • Generation starts automatically after reset
  • Pattern loops continuously
  • The START pin is not shown on the symbol

When Auto Start is disabled:

  • The START pin appears on the symbol
  • Generation begins on rising edge of START
  • Pattern plays once per START pulse

Timing

Parameter Value
Latency 1 clock cycle
Throughput 1 sample per (PRESCALER+1) clock cycles

Resources & Timing

  • Latency: 1 clock cycle

  • Throughput: 1 sample per (PRESCALER+1) clock cycles

Uses Block RAM for ROM storage. Memory usage depends on Memory Size and Bit Width settings.