Walk to the introduction to VHDL in this lecture I'm going to introduce and explain the HDL and what
it is use for fish.
This stands for the h s I see hardware descriptive language and VHS I see stands for very high speed
integrated circuit.
And what my HDL is used for is to describe the actual physical circuit and that's exactly what we're
doing with the HGL we are describing a circuit using code or VHDL to physically describe how we want
that digital circuit to operate.
Let's just talk a little bit about the history HDL VHDL was developed in 1981 by the Department of Defense
and the reason they created the HDL was they develop this as a way to address the hardware lifecycle
crisis of electronic systems.
If you have a circuit board with a lot of integrated circuits and with electronic systems and Atrox
today we know that every so many years that here the current components are using go out of date.
They have newer the latest and greatest in the Department of Defense wants the latest integrated technology.
However it becomes very task for very hard to re engineer or relay out a board.
So the VHDL is used as a way to replace that you can put an FPGA a C PLB on your circuit board.
And so as standards change and electronics evolve you can implement a new program to run on there and
kind of mitigate that risk.
And the department offense gave away all rights of the language to the Tripoli the Institute of Electrical
and Electronics Engineers.
And so they're the ones that are in charge of the VHDL language defining the standards.
So on and so forth.
Different devices that use VHDL are one is PJ's which are field programmable get arrays and this class
that's what we'll be using with our different villain boards will be having an FPGA on there that we're
going to be writing the HDL code to describe the circuits that will be operating on these FPGA.
Then you had a CPA L.D. which is a complex programmable logic device.
These are in a way you can think of them as a smaller more less capable FPGA and FPGA is a lot more
powerful.
A CPO is less powerful then we have a sick which is an application specific integrated circuit.
This would be anything like if you have a shift register built into an icy chip or a processor microprocessor.
All these are considered basic.
This is a chip that has a specific designated function and you can use VHDL to write how you want the
circuit inside of it to work.
And then there's different tools you can use to take your VHDL and turn it into transistors and gates
and implement it actually on the physical silicone.
So we're talking at PJ's Or C A.
Let's do a little comparison between the two Apogees their design using logic blocks.
They have a much higher logic capacity than a CPD.
And typically we use an FPGA for a much more complex or high bandwidth designs.
They have multiple memory.
When you power off the FPGA loses its configuration.
So every time you kind of power back on your FPGA has to read in the configuration file whether it be
from J tag or in on chip flash or an SD card or whatever type of memory device that's going to load
the configuration file into that Pejic and typically beings that FPGA is more powerful and more capable
they are more expensive and Sebille these now CPB may have less capacity than FPGA.
They are typically used when you have a simpler less complex design.
However they do have nonvolatile memory meaning if you turn the CPV off and turn the power back on the
Sebille the remains that configuration of ice so you don't have to have an external memory device.
All of that TPL d to load back in every time you turn the power back on.
And typically they're are more cost effective than apogee.
And you have a very simple basic design and you can fit it on a.
You are more apt to do that.
However if you think in the future your design is going to grow or you want to add more to that your
going to go.
PJ It's a lot more powerful and to major manufacturers of FPGA and speel these are Xilinx and Altera
some key points.
The HTL is not a programming language.
We're not actually programming.
PJ we're writing a configuration file or writing or describing how we want an actual physical digital
circuit to run on the FPGA.
And along with the same point VHDL is software it is used to describe the hardware the software would
run on.
So if you have a processor you would write VHDL to describe that processor and then you could write
software that would run on the processor where the actual synthesize the compiler runs to the code and
constructs the gate specified in the VHDL code and it limits them on the target logic device and the
top two manufacturers at and CPM these or Xilinx and Altera
that is VHDL to a high level.
Now let's get started getting into the details.