Practical Design Projects Utilizing Complex Programmable Logic Devices (Cpld)

Abstract NOTE: The first page of text has been automatically extracted and included below in lieu of an abstract Practical Design Projects utilizing Complex Programmable Logic Devices (CPLD). I. Introduction This paper describes the use of programmable logic-based design in junior/senior project applications in electrical and computer engineering programs. It is shown that a variety of projects can be conceived using a complex programmable logic device (CPLD) as a central controller of analog to digital (ADC) and digital to analog (DAC) components for interfacing with a number of sensors and transducers including an ultrasonic ranger, a temperature sensor and an RC servo. The flexibility of the CPLD-based design and its cost effectiveness are highlighted with design and programming examples used in actual projects assigned to junior and senior electrical engineering and computer engineering students. II. Programmable logic basics A. Typical Design Methodology A slew of programmable logic devices have existed for several decades, initially in form of programmable and reprogrammable read-only-memories (ROM-EEPROM) and later in form of programmable logic devices (PLD) and field programmable gate arrays (FPGA). A variety of applications such as programmable industrial controllers and dedicated special purpose circuits have used these programmable devices. The most recent advances in programmable logic have produced an even more elaborate method which allows programming of desired interconnections between pre-built modules such as registers and complex logic circuits, including embedded microprocessors and digital filters modules. In their modern day configuration, FPGA’s offer the highest level of logic density (up to eight million “system gates”). By contrast, the so called, programmable logic devices (CPLD), with lower circuit densities (up to 10,000 logic gates) and very predictable timing characteristics, are better suited for critical control circuit design applications. A typical configuration of a CPLD-based circuit design is depicted in Fig. 1. This configuration allows for a variety of circuit design assignments which integrate “analog” and “digital” signals as well as sensors, actuators and transducers. In this depiction, the central “intelligent” component is the CPLD, which decides on actions to take based on the information sensed by the sensor-to-voltage transducers such as temperature, pressure etc… sensors. The signals provided by the transducers are digitized by the ADC and fed to the CPLD for processing. In addition, digital signals can be sensed directly by the CPLD through its input output (I/O) bus lines. Various actuators can also be controlled by digital control of a DAC.