Replacing obsolete video game circuits with Xilinx CPLDs

By In Choi, Retro Devices Technology
pldesignline.com (October 08, 2008)

Abstract

In this article, designer In Choi describes a project for his home business in which he replaces a defective part in a 1980s game system to show his full-time employer that they can adopt a methodology using Xilinx programmable devices to replace a range of parts that other semiconductor vendors are no longer producing.

Introduction

Parts obsolescence is nothing new, but it has attracted more attention recently, particularly in the semiconductor industry. Sometimes chip companies no longer produce parts for older products; others go out of business.

Although no single optimal solution exists, you can typically manage parts obsolescence using one of three methods:

• Find a form, fit, and functional substitute.
• Redesign the subsystem containing the obsolete part.
• Replace or redesign the entire system.

From a practical perspective, the last two methods are generally too expensive; it would probably be more cost-effective to replace the subsystem or the entire system.

Thus, the first method is the most practical, and we'll show how we at Retro Devices Technology did it using a Xilinx XC9536XL CPLD – specifically targeted for 5V transistor-to-transistor logic (TTL) gates and digital logic functions – to replace a 74LS32 microcircuit in the PCB of a 1980s video game system called Vectrex. For the sake of this project, we are assuming that the 74LS32 is obsolete.

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