cpe229_lec22 - CPE 229 Course Notes: Lecture 24 Copyright:...

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- 1 - CPE 229 Course Notes: Lecture 24 © Copyright: 2005 Bryan Mealy I/O Stuff Without input and output capabilities, all the hardware and software that we’ve come to know as a computer would be useless. In other words, I/O is an important matter. As was shown in the previous set of notes, the PicoBlaze microcontroller was designed to be a generic computer. In particular, its I/O capabilities were simple at best. This simplicity required that other hardware be included with PicoBlaze in order to extend the devices basic operations to include to real I/O. This was done with the now famous VHDL wrapper which was nothing more than some VHDL code that induced registers for mapping output values and data selectors for input values. This set of notes will design similar hardware on a block diagram level to extend the operation of PicoBlaze in a hopefully intelligent manner. Basic Design Matters There is a world full of digital devices out there that are just waiting to be controlled by microcontrollers such as PicoBlaze. Keep in mind that PicoBlaze is a versatile digital device in that the hardware can be easily reprogrammed in order to control just about any other digital device out there. This is good news because there are about a bajillion different devices out there waiting for you to include them in your next design. This is a basic device interface problem with a solution that has a relatively generic approach. After you’ve identified a device that you want to control with PicoBlaze, there are three basic steps required which are outlined below. 1. Define device interface requirements: Read through the datasheet for the peripheral device in order to define which signal on the device will be used to communicate with the microcontroller. These signals are essentially control and status signals: the control signals are used to control the peripheral device and the status signals are used to communicate status information to the microcontroller. After all, why do you think they call it a microcontroller? 2. Design required interface hardware: The PicoBlaze microcontroller is a generic design so you’ll probably need to design special hardware to facilitate the interface. This is basic hardware design that is similar to the previous design that we’ve worked with, namely the wrapper stuff. 3. Design required firmware to interface with hardware: The step is often referred to as writing the device driver . In this context, a device driver is nothing more than some software (or firmware) that is used to control some hardware. This is simply a fancy name for writing some code that does something useful in the context of a real system. Interfacing PicoBlaze to an EPROM One of the drawbacks of PicoBlaze is that it only has memory for instructions (and no memory for data). This lack of data memory could be viewed as a severe limitation in the basic PicoBlaze microcontroller.
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cpe229_lec22 - CPE 229 Course Notes: Lecture 24 Copyright:...

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