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implementation of vhdl code on cpld

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vimalpandey

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I had written a VHDL code for 16 bit microprocessor and i would like to implement this on CPLD. And i would like to know can i made my own PCB or i have to purchase the ready-made board. If it is possible what are the necessary interfacing devices.
 

allsey87

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Okay, first up - theoretically you can synthesis your 16 bit micro controller design for implementation on a CPLD, practically speaking - I think your going to have a very hard time getting it to fit, unless your CPLD is considerably larger than what I'm thinking of (for example, Xilinx Coolrunner II).

Also consider, how are you going to put your compiled code on this device, implementing ROM on a CPLD is very inefficient, and if you use some kind of external memory which requires connections for address and data, you are going to run out of pins very quickly on that device. Typically FPGAs are far more suited to this kind of application.

Now with making your own PCB, you can... but consider: doing this with CPLD is possible but as discussed above, probably won't work with your application. Using an small FPGA (like a Actel Ignoo Nano) is a possible alternative, but be warned, this is not for the beginner circuit designer it is a very challenging endeavour. See the following video blog which explains the process and gotchas to appreciate the depth of designing circuits with FPGAs : EEVblog #193 – FPGA Implementation Tutorial | EEVblog - The Electronics Engineering Video Blog

There are also many development boards available, which I could not recommend to you more. Digilent have many boards which will suit your purpose, the cheapest and the one I would reccomend for your project would be the . They also do great academic discounts if your in uni.
 
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TrickyDicky

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I would buy an eval board. Making your own PCB would be very time consuming.

And are you sure you want a CPLD and not a FPGA?
 

vimalpandey

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Thanks for your help.Tell me one thing what is cost of FPGA? Can i made my own PCB using FPGA
 

allsey87

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@vimalpandey FPGAs can cost anything between $20 to $2000 for high end devices. But you don't want to buy an FPGA, take my word for it, buy a development board like the BASYS2 which comes with everything you need - this is probably the only chance you'll have at finishing this project of yours on time.

---------- Post added at 22:25 ---------- Previous post was at 22:17 ----------

Also, from the perspective of cost, making a PCB with an FPGA on it requires very very fine traces and vias. This is incredibly expensive, far more costly than the FPGA device itself.

---------- Post added at 22:26 ---------- Previous post was at 22:25 ----------

watch the video already: EEVblog #193 – FPGA Implementation Tutorial | EEVblog - The Electronics Engineering Video Blog
 

RetroTechie

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Basys2 board doesn't have on-board RAM (apart from whatever small block RAM is in the FPGA). That would be a big drawback for CPU-related projects.

Thanks for your help.Tell me one thing what is cost of FPGA? Can i made my own PCB using FPGA
Low-end FPGA's aren't expensive but current FPGA's don't come in DIY-friendly housings. So problem is not price of a bare chip, but building something with that. Given the wide range of FPGA boards available today, (trying to) produce your own is just big waste of time... Exception might be if you're designing something that's meant to be produced in large numbers.

For what you'd want/need on a board: some hints here. Ultimately it's just a case of your budget & what you want to do.
 

mrflibble

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Can i made my own PCB using FPGA

If you have to ask that, the answer is no. Seriously. You are better of buying a ready made development board.

The three links in RetroTechie's post should get you started.
 

allsey87

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@RetroTechie - 16 bit microcontroller + guy that doesn't understand the implications of designing PCBs with FPGAs... this sounds alarm bells in my head saying "2nd or 3rd year undergraduate project", the code that is going to be executed will most likely be less than 100 hand coded assembly instructions and will easily fit inside the blockRAM provided by the Spartan 3E. Not too mention this approach is much easier for a beginner than trying to interface an external device...

@Vimalpandey is the board for you mate, it is the cheapest I've seen and still has decent specs. It should get your project up and running quickly...
 

vimalpandey

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@allsey87-- you are right this project is of B.Tech 4th year students. They are working under me but problem is that institute wants that they should made PCB, that's why i m asking for that. If there is any other way then please suggest b/c i know that implementing FPGA or CPLD on PCB is tough job.
 

allsey87

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Tough is understatement, and remember the cost to get these boards (one for each group of students) fabricated is going to be well and truely above what you faulty is willing to allocate to you should you go down this path.

I would split the project into two parts.

Part 1: implement the 16 bit microcontroller on the development board BASYS2
Part 2: Make a simple PCB that plugs into the PMOD connectors which provides some additional IO, i.e. a stepper motor interface or a light level sensor which the students can then make an assembly program to demonstrate their work.
 

FvM

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With some restrictions, it's possible to implement a FPGA in QPFP package (0.5 mm pin distance on a double layer PCB with 150 um structure size. A four layer board would be preferred however for reasonable wiring. The devices can be fairly hand soldered.

Although I have done it quite often for prototypes, I'm hesitating to suggest it for a students project. There should be at least support from a experienced technician. And you absolutely need professionally manufactured PCBs with through plating and solder mask and good solder tools.
 

RetroTechie

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@allsey87-- you are right this project is of B.Tech 4th year students. They are working under me but problem is that institute wants that they should made PCB, that's why i m asking for that. If there is any other way then please suggest b/c i know that implementing FPGA or CPLD on PCB is tough job.
You have a group of students, a 16 bit CPU as sample project, and institute expects students to design and/or produce their own boards with CPLD or FPGA? That's crazy, they have their heads on backwards... :lol: Either:
  • Pick a simpler project a la some blinking LEDs, do it using small CPLD in hand-solder friendly package like PLCC. Then students could design (perhaps even produce) their own boards if that's deemed important.
  • Or use big CPLD / small FPGA, get institute to drop 'produce your own board' requirement, and have professional 3rd party supply boards. Design of that board (and perhaps soldering CPLD / FPGA onto it) could be done as a student project, but that would significantly increase the overall project size (& require supervision by experienced technician / designer, like FvM said).
  • Or get ready-made CPLD / FPGA development boards & focus on project(s) to implement.
 
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