Introduction to Bare Minimum Circuitry to Boot OSD335x

Published On: June, 29, 2017 By: Eshtaartha Basu | Updated: July 18, 2018 by Cathleen Wicks

Introduction

The objective of this lesson is to help you become familiar with the bare minimum setup required to boot the OSD335x and getting it ready to execute software. This lesson will consist of a series of articles which will walk you through every step of the design process. We start from specifications and guide you through every step till debugging the manufactured Printed Circuit Board (PCB). The lesson will conclude with a PCB that verifies the design by putting together everything that was taught.

To boot the OSD335x in its minimal configuration, we will need:

Power circuitry
Clock circuitry
Reset circuitry
Debugging/Programming interface (JTAG interface)

To make our design more functional, we will add a couple of buttons, LEDs and a peripheral header to allow us to better test our completed design.

A block diagram of this setup is shown in Figure 1. We will discuss each of these concerns in separate articles to have a better depth of understanding of each topic. The articles are as follows:

These articles as well as the entire OSD335x Design Tutorial can be downloaded here.

Prerequisites

This article is a part of the broader OSD335x Reference Design Lesson Series which consists of a series of articles designed to help you become familiar with the circuitry required to use the OSD335x.

We recommend reading the introduction article Introduction to the OSD335x Reference Design Tutorial Series before this one because his article builds upon the foundation outlined in it.

CAD Environment Setup

Before proceeding with the articles, let’s understand the Autodesk Eagle design environment which we will be using.

For this design, we are going to create a PCB with the following parameters:

Board Size: 2500mil x 2000mil (2.5inch x 2inch)
Number of layers: 4 layers.
Trace width: 6mil (approx. 0.15mm). Since power traces generally carry more current, we will be using larger traces (at least 15mil or 0.4mm) for them.
Trace spacing: 6mil.
Minimum drill and via size: 12mil (approx. 0.30mm) drill and 24mil (approx. 0.60mm) finished via diameter (i.e., 6 mil annular ring).

Using these standard rules will help us reduce manufacturing cost. For your design, you are free to select the appropriate rules for your manufacturer and components that suit your design.

All design files for this lesson can be downloaded here.

Library Setup

Octavo Systems provides an Eagle library OSD3358_BAS_RefDesignParts.lbr that contains the schematic symbol and footprint for the device. This reference library can be downloaded here.

It is good practice to create your own Eagle Library for each design and copy all parts used in the design into it. For this design, we have created the library OSD3358_BAS_RefDesignParts.lbr.
Setup the Eagle library path to the location of the Octavo Systems library file and copy the device OSD3358-512M-BAS into your new library.

Schematic setup

Open a new schematic file and name it appropriately.
Make sure to use the OSD3358_BAS_RefDesignParts.lbr library in the schematics.
From the library, add the OSD3358-512M-BAS symbols to the schematic as shown in Figure 2. The OSD3358-512M-BAS symbol will easily fit into A3 size sheets. In the design files, all four A3 sheets are consolidated into a single Eagle sheet so that we can use the free version of the tool while still allowing the schematics to be easily viewable while printing.

Figure 2 OSD335x symbol arrangement on schematic

Layout (Board) Setup:

The layer stack up is shown in Figure 3. We’ll be using Top and Bottom layers for signal routing. Route2 layer acts as power plane (We will be connecting it to an appropriate power output pin of the OSD335x later). Route15 layer acts as ground plane.