Fpga

[AtomSoft]

FPGAs seem so useful... do they make small versions ? Like what if i wanted to implement custom logic for instance...

I wanted to make a Multiplexor with some Invert Logic and a OR gate. It would suck to have to use a 100pin TQFP

 

[RichTheDude]

FPGAs seem so useful... do they make small versions ? Like what if i wanted to implement custom logic for instance...

I wanted to make a Multiplexor with some Invert Logic and a OR gate. It would suck to have to use a 100pin TQFP

This is the job of CPLD's . I tend to use Lattice for CPLD's (M4a5 for 5V, ispmach4000 for 3.3V) as not many companies do large 5V CPLD's anymore (the 64 macrocell part is good and cheap to start with). I still use CPLD's a lot on microcontroller projects where I need some logic, and in the devices I develop an extra £5 for a CPLD is not going to be noticed. The benefits are reprogrammability, much faster than 74 series logic (the ispMACH is good for 400 MHz), less board space and IC count than using 74 series logic, and if you route some of your pins through a CPLD you can use it as a pin mux, and use the CPLD to change pin mapping (I only do this for a few pins usually mind)

https://www.electro-tech-online.com/custompdfs/2011/07/ispm4a.pdf
and
https://www.electro-tech-online.com/custompdfs/2011/07/DS1020.pdf

Both are availble in small packages (the PLCC 44 pin one is nice, you can knock a board up on vero/pad board!). Beware, as mentioned before CPLD's are tiny in comparison to even the smallest FPGA, and they are lot more costly for the amount of equivalent gates you get.

A 64 macrocell device should easily be able to do your multiplexor and combinational logic. This http://elm-chan.org/works/avrx/lattice.png cable definately works with 5V devices. I built that and a M4A5-64/32 home brew board when I was starting out learning VHDL

 

[AtomSoft]

AWESOME!!! So do you think i should play with CPLDs first? I think it would help me understand on how logic works and get my feet wet before jumping in to the FPGA Pool

 

[AtomSoft]

OK found at mouser:
https://www.mouser.com/ProductDetai...=sGAEpiMZZMuJNuO2s1hGZEbAxui0DvQNfPuHKQmPXrw=

And IC for cable:
https://www.mouser.com/ProductDetai...=sGAEpiMZZMuiiWkaIwCK2RTxPVPWGz6WxxzMIIu9lOg=

 

[AtomSoft]

Im not a PLCC fan but i seem to have all of these in one of my organizers...

 

[AtomSoft]

I can make a PCB at home and if it works with the CPLD i buy then ill get the PCB made pro... will be cheap

 

[RichTheDude]

Those parts are fine, but I built mine using TH (a lot cheaper than getting boards made, which was important when I was a student studying VHDL. I can now make single sided boards at home thankfully!).

A CPLD will limit your project scope (complexity), but as a tool for hands on learning VHDL I think they are fine. A lot of people recommend learning FPGA's straight out as they are much bigger devices, and include more complexities in the design process (like the dreaded phrase "I have not met timing").

This board is of similar spec to what you can do with the aforementioned parts

**broken link removed**

(Are links to things like this ok or frownded upon, apologies if this is bad thing!)

 

[AtomSoft]

I can do double sided PCBs at home so SMT parts are fine for me heh... Cant wait to get started but have to Ill order parts on Monday. Ill be sure to order a few CPLDs instead of one this way i wont have to worry if i screw one up somehow

 

[AtomSoft]

I have a cool idea for my first FPGA project. Since i always wanted to get into VGA stuff i was thinking about making a FPGA VGA Buffer of some kind where you send the entire screen to the FPGA .. like a background image. and then it would constantly refresh that data for you until you send some new info and only after all data required is input the screen will change. Something simple like that. I hear VGA is dead simple of a FPGA.. also since it can go so fast i can have it access parallel RAM for storage of the screen.

Or even a SD card at full speed. So one can load images ...

 

[AtomSoft]

https://hackaday.com/2008/12/11/how-to-programmable-logic-devices-cpld/

Seems like a nice read

 

[AtomSoft]

Ok so answer this... with a CPLD can i create just about any 74xxxx series IC? Like buffers and Transceivers ?

 

[RichTheDude]

Pretty much, buffers would be just hooking up an IO pin to another. Trasceivers would be easy too (you can have bidirectional ports, and make them high Z).

I was thinking perhaps open collector (like 7407) could not be done, but then I realised I was thinking nonsense, and in fact I have used a CPLD in an open collector manner in the past. It's just a tri statable output, with the input to the io buffer tied to logic 0 only (toggle the tristate control to pull low or let it go high Z).

Would still have to be careful of the current limitations of the IO pin though and going over the voltage rating of the IO pin in the off state. I used this to make crude monostables...

 

[AtomSoft]

ah, yeah.. thanks.

 

[Sceadwian]

It only gets more complex from there =) Wait till you try to do logic timing from multiple separate elements.

 

[AtomSoft]

Ah found this:

https://www.electro-tech-online.com/custompdfs/2011/07/an8082.pdf

Last page has schematics... would be simple for me to make.. Ill get it sent out to make . While they dont make that Switch (STG3690QTR) anymore i found:

https://www.mouser.com/ProductDetai...GAEpiMZZMtxrAS98ir%2bs6ERF3TSO9w3xdp11UxseCI=

which looks similar enough to get the job done

Image made by me

Was actually reading the pdf and found

The FT2232D device is not only a convenient solution to programming JTAG devices over USB but, it also provides
development and debugging options as well. The schematic in Appendix B, shows an analog MUX (U3) which is
used to divert the signals from channel A to either a JTAG chain or an I2C bus. Pin 16 of U1 can then be controlled
by the host software to switch between the JTAG chain and the I2C bus. FTDI provides the drivers and example
files of how to configure the FT2232D to interface with the I2C bus.

So i can omit that part if planning on using it for JTAG only

 

[AtomSoft]

It only gets more complex from there =) Wait till you try to do logic timing from multiple separate elements.

When I get into that ill be sure to SCREAM here

 

[Sceadwian]

You might want to add RichTheDude to your rolodex Atom, as far as I know he's one of the few members here that have ever professed any even moderate understanding of FPGA design. It is definitely a world apart from the typical, and that's coming from a hobby that is a rarity itself.

 

[AtomSoft]

heh Yeah, Ill be sure to add him as a friend right now... Im so tired... need a break but there is nothing else to do

 

[RichTheDude]

Thanks for that link AtomSoft, I brought myself a chinese clone JTAG for lattice (cypress FX2 based) some time ago to use on my laptop. That would be a great solution for a little dev board or as a cable on its own.

Slightly off topic here, but people doing any form of electronics seems a rare breed in the UK people just do not seem interested. Is it the same in the US?

The arduino crowd is bringing people in, but the ones I have met seem to stick to the arduino for everything (I have seen one used in place of a monostable the once), rather than venturing out and trying other forms of electronics. Glad it's bring people in, and some of them must venture beyond the arduino .

I'm in my mid to late 20's and out of all my mates that I went to uni with, I think there is only myself that's stuck with electronics (FPGA, CPLD, analogue, and embedded), one guy does embedded software and all the others do PC side software...

I am doing a lot of hobby electronics projects in my spare time lately as my lady friend is about 170 miles away

 

[AtomSoft]

Your welcome for the link, I plan to order the parts this coming Monday. Thats when i get paid (well saturday but monday ill order)
Heh yeah, everyone into electronics here is also slighty far. There are groups and gatherings which i want to attend. But its about a hour away which isnt too long but still is... I wish i had some close pals to do this stuff with. get other people thoughts and such. im 26 about to be 27 on Aug 7 this year... few weeks really heh.. I live with my GF/Wife... not married but together for 9 year this October