FPGA beginner - Page 1
Forum section: electronics / projects

author: gonnafail
author_rank: Contributor
timestamp: November 25, 2010, 05:40:12 am
content: I have an upcoming project where I will need to receive, decode, then retransmit HDMI video signals. I plan on using the Texas Instruments HDMI transmitter receivers and have come to the decision that this will need to be done with an FPGA. The problem is I have very little experience with FPGAs. I have done some code modifications on boards at work and I took a couple of courses at school on VHDL. I was wondering if anyone had any good resources for learning FPGA development. Either Alterra or Xilinx is fine. Ideally I would like a reasonably priced Development board with a series of lessons meant to be used with it to get me started. The main requirement being that the FPGA on the dev board be capable of HDMI input/output.I have found a lot of various development boards out there but most seem to be quite expensive with very little resources for a beginner. I am hoping to find something less than $800 CDN with a decent level of support behind it.

author: allanw
author_rank: Frequent Contributor
timestamp: November 25, 2010, 08:10:38 am
content: I started an FPGA project recently and found this board to be very cheap, at least at academic pricing.http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,836&Prod=ATLYSIt has HDMI.

author: joelby
author_rank: Frequent Contributor
timestamp: November 25, 2010, 12:11:15 pm
content: There's a nice book called FPGA Prototyping Using Verilog Examples (also available in VHDL), which was written for Digilent's Nexys2 board, but some of the examples might apply. The ATLYS looks great for your application, gonnafail, and also mine - thanks allanw, I might actually redesign the thing I'm in the midst of making for the Nexys2 to use it, because it has a nice impedance controlled, matched differential pair connector. The Nexys2's expansion port has arbitrary length traces and differential pairs are scattered every which way!

author: joelby
author_rank: Frequent Contributor
timestamp: November 25, 2010, 02:07:50 pm
content: Just thought I'd mention (because I just discovered it myself) that Xilinx has some interesting free resources online:http://www.xilinx.com/training/free-video-courses.htmhttp://www.xilinx.com/university/students/index.htm(click Resources)

author: gonnafail
author_rank: Contributor
timestamp: November 25, 2010, 03:48:48 pm
content: I am going to have to take a closer look at that Atlys development board but that looks to be perfect for my needs. Quite reasonably priced too. I looked at a lot of development boards and was having a hard time finding one with two HDMI ports, this one has four! I had also stumbled across the Xilinx training, Altera has similar here:http://www.altera.com/education/training/curriculum/fpga/trn-fpga.htmlDoes anyone know of a good support forum? Book recommendations? any other information on FPGA design? Advice for beginner?Thanks for the information already given, that has been very helpful already.

author: joelby
author_rank: Frequent Contributor
timestamp: November 25, 2010, 04:19:35 pm
content: Xilinx hosts its own forum, which seems to be heavily used and has some very helpful contributors.fpga4fun.com has some interesting projects for getting started with, though I found that reasons for using particular coding styles weren't always explained in enough detail (but other resources filled in the gaps).The comp.arch.FPGA news group is also surprisingly busy:http://groups.google.com/group/comp.arch.fpga/topics

author: allanw
author_rank: Frequent Contributor
timestamp: November 25, 2010, 05:00:22 pm
content: Quote from: joelby on November 25, 2010, 12:11:15 pmThis will be long but I spent a while researching connectors...Unfortunately, to buy the VHDCI mating plug they used on the Atlys board, you have to get it shipped from Taiwan with a $100 shipping charge...There are alternatives, but they are a bit strange:Samtec sells an edge-mount plug:http://samtec.com/ProductInformation/TechnicalSpecifications/Overview.aspx?series=VHDCPFor this plug, I believe the differential pairs are set up so that one signal of the pair is on the bottom layer and the other is on the top layer. So this means you'll have one via change imbalance. The connector is about $10, but you can get a few free samples which is nice.Molex also has one:http://www.molex.com/molex/products/datasheet.jsp?part=active/0714253001_IO_CONNECTORS.xml&channel=Products&Lang=en-USBut the mounting method is a bit weird. I think it's through-hole but you need to get rectangular slots cut into your PCB.I just found out about this board:http://www.xilinx.com/products/devkits/EK-S6-SP601-G.htmIt has the industry standard FMC connector on it, but you have to pay $100 to buy the specification just to see the pinout. Shoot, if I'd known this board existed I would have bought it instead of the Atlys.

author: joelby
author_rank: Frequent Contributor
timestamp: November 26, 2010, 01:30:30 am
content: Quote from: allanw on November 25, 2010, 05:00:22 pmIt's odd that Digilent don't stock this connector - they sell the Nexys2's Hirose FX2 connector. I recommend buying the VHDCI expansion boards and unsoldering the connectors! If you get the breadboard one, you end up with a nice big breadboard for only a few dollars more than the connector would have cost anyway.QuoteHmm, that looks like an IDC connector to me. How aboutthis Molex part? Unfortunately it looks like element14 only sell the receptacle connector - I assume that the expansion board uses the plug. Would you mind confirming this by looking at the edge of your board, before I buy something I don't need?Samtec also do athrough-hole version, but it's more expensive and less in-stock than the Molex one, and also a receptacle.

author: gonnafail
author_rank: Contributor
timestamp: November 26, 2010, 01:46:26 am
content: QuoteCorrect me if I am wrong but isn't this the connector available at digikey for about $15?http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=WM7320-NDWorst case you could always buy one of their expansion boards for $30-$40 and steal the connector off of that. I would hate to be the one doing all the desoldering on that but I would if it saved me spending more than $100 on a connector.

author: joelby
author_rank: Frequent Contributor
timestamp: November 26, 2010, 01:54:21 am
content: That looks like the receptacle rather than the plug. It doesn't look like anyone makes a board-mounted plug, other than Digilent's not-stocked-by-anyone supplier, so it might be necessary to just use two receptacles and a VHDCI cable assembly.

author: allanw
author_rank: Frequent Contributor
timestamp: November 26, 2010, 02:24:39 am
content: VHDCI male-male cables are insanely expensive since they're intended for the enterprise-y SCSI market. The cheapest ones you can buy from regular stores are like $80+.I sure as hell am not going to pay $30 for their prototype boards just to desolder the connector.I've decided to just design for the Samtec edge-mount connector since they're only $10 and live with the extra via change. It shouldn't make a huge difference. One extra disadvantage is that the product datasheet recommends using a thickness of 0.039" instead of the regular 0.063". But I'm sure a little bending of the pins will make it work OK...edit: Emailed Digilent with:"It's rather unfortunate that you do not sell these connectors. How can you expect people to develop their own boards for the Atlys for prototyping use if the only option is to get the VHDCI plugs direct from Taiwan? I was quoted a shipping charge of $100."

author: joelby
author_rank: Frequent Contributor
timestamp: November 26, 2010, 02:31:21 am
content: Quote from: allanw on November 26, 2010, 02:24:39 amI just had a quick look on eBay and inexpensive (well, <$50) VHDCI connectors abound. There are even some that come inridiculous lengths.Making up a short cable with two IDC connectors should be straightforward if you have a vice, and only cost you a bit more than 2 * $10, plus a $10 receptacle, but unless Digilent start stocking the connector I think I'll have to use the Samtec part toogonnafail, sorry to get off topic here - hopefully with all the HDMI ports on board you won't need to worry external expansion!

author: gonnafail
author_rank: Contributor
timestamp: November 26, 2010, 03:23:36 am
content: gonnafail, sorry to get off topic here - hopefully with all the HDMI ports on board you won't need to worry external expansion!No problem, I always welcome a healthy discussion. While heading off topic at least this thread has remained "troll free". In adding to the connector issue from the Atlys reference manual which you can download from the previously linked site at the top of the tread. It shows the board as having the "male" type plug in which case the $15 receptacles are what you need. If anyone has this board it would be great to hear confirmation from them on this though.It is true that with all the HDMI ports I myself will not need the expansion, at least not for this project but it is something worth noting before purchasing as who knows what you will be doing in the future. The way I look at it if they are able to sell expansion boards for $30 with the header then there must be a reasonably priced source out there somewhere. It would be much more convenient and make sense if you could buy these connectors from digilent seeing as they are supplying the connectors to other boards. That being said if I were designing an expansion board and the connector is one that I could get from digikey, I would order it from them with all the rest of my parts and not bother with a second supplier. This could be why they have decided not to carry this specific connector if it is easily available from other distributers.

author: allanw
author_rank: Frequent Contributor
timestamp: November 26, 2010, 03:27:26 am
content: Perhaps they get the boards manufactured and assembled directly in Asia without having to stock all the parts themselves. That would explain why they do not sell the connectors. Hopefully if they get some customer demand for them then they'd at least consider it.I will be receiving the board on Monday and I will confirm. However, from the small pictures on their site, it appears like it is indeed the receptacle on the main board and plugs on the prototyping boards.

author: joelby
author_rank: Frequent Contributor
timestamp: November 26, 2010, 03:33:07 am
content: Quote from: gonnafail on November 26, 2010, 03:23:36 amDo you mean the diagram on page 17? You're right, and it would make sense for them to do it this way. Hopefully I'll have mine on Monday or Tuesday and will report back if allanw hasn't already.QuoteTrue. While the Hirose FX2 connector is available from element14, there are a bunch of different companies making VHDCI connectors. I don't see why Digilent wouldn't just sell one with their own mark-up, though. Chances are they just haven't got around to it yet, because it's such a new product.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 26, 2010, 11:40:22 pm
content: QuoteWTF?Can't see how they expect this to really catch on of they charge for the pinout...and anyway isn't it in the schematic of any devboard that has it anyway... at least the subset of the pins that the board implemenrs, which si all you;re going to need anyway?

author: allanw
author_rank: Frequent Contributor
timestamp: November 27, 2010, 12:35:29 am
content: Yeah it doesn't really matter for the companies I'm sure and $100 isn't much compared to the product cost of anything high performance enough to use the connector. It is pretty popular:http://www.xilinx.com/products/boards_kits/fmc.htm. Also, I believe the connectors are around $5 from Samtec. Anyway, this FMC connector is on the Xilinx board and I don't think they provide a schematic.Altera has their own connector standard which is free.

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: November 27, 2010, 11:10:41 am
content: Quote from: allanw on November 27, 2010, 12:35:29 amSchematic appears to be here :http://www.xilinx.com/support/documentation/boards_and_kits/xtp051_sp601_schematics.pdf

author: allanw
author_rank: Frequent Contributor
timestamp: November 27, 2010, 07:07:03 pm
content: Ah you're right. The basic pin-out info is there but there might be some important info regarding via placement and other PCB layout considerations when using the FMC connector at high speeds.I did some more research and found out that the FMC connector is $20.

author: allanw
author_rank: Frequent Contributor
timestamp: November 30, 2010, 04:26:14 pm
content: Got the Atlys board today. I think the connector on it is the receptacle. I measured the height of the protruding metal part and it's about 3.5mm. The plug is 4.7mm high but the receptacle is 3.5mm high. Here's some pictures of it since they don't have any detailed pics on their website.Oh and it even comes with a nice plastic case too.

author: joelby
author_rank: Frequent Contributor
timestamp: December 01, 2010, 12:09:54 am
content: Sod, that does look like the receptacle. Digilent wrote back to me to say that they don't have any of the plugs in stock and suggested a Molex IDC connector. Until they do, I think I'll have to go the cheap (and hopefully short) eBay SCSI cable route!Aside from shipping, how much did the Taiwanese company quote for the plug? Maybe we could do an eevblog group buy! Sometimes it's possible to convince manufacturers to use the regular postal system rather than a courier, too.

author: gonnafail
author_rank: Contributor
timestamp: December 01, 2010, 12:46:59 am
content: I have found this connector available at mouser:http://ca.mouser.com/ProductDetail/Molex/71425-3001/?qs=x6EjVpvqMVNx/mxf%252b/nSeg%3d%3dor at Arrow:http://app.arrownac.com/aws/pg_webc/0,1086,,00.html?application=SEARCH&event=1009&search_token=714253001&search_criteria=match_begins_with&match_in_stock_only=NO&=&rows_to_display=10&limit=10&full_domain_name=app.arrownac.com&super_neda=&start_index=0&search_type=click_throughI have never used Arrow so do not know what they are like. I have used Mouser once before and they were pretty quick but shipping/duties was quite expensive into Canada. That was quite a few years ago now since I have stayed away from them since. Possibly it is better now.With these connectors you would need to use some wire to the board and would not be able to board mount them. I have yet to find the board mount connectors that are used on the daughter boards.too bad about it being the receptacle on the dev kit. I thought that the data sheet clearly showed it being the male connector.

author: allanw
author_rank: Frequent Contributor
timestamp: December 01, 2010, 12:48:31 am
content: Arrow's pretty good. Their prices are really low for random items. Shipping is pretty cheap too.I'm going to just go with the Samtec connector. Getting a sample.

author: joelby
author_rank: Frequent Contributor
timestamp: December 01, 2010, 12:51:00 am
content: Quote from: allanw on December 01, 2010, 12:48:31 amHow are you planning to connect it to your board? A ribbon cable soldered to your board, or will you try to PCB-mount the IDC pins?

author: allanw
author_rank: Frequent Contributor
timestamp: December 01, 2010, 01:07:29 am
content: I'm puzzled by the Molex plug. How's it supposed to mount to a board? Maybe if you were able to drill and plate rectangular holes...The Samtec is designed for PCB mount, so I was going to just mount it on the edge of my board as their pcb layout recommendation says. I'm getting a sample to see if it'll work on standard 0.063" thick boards. Their document recommends 0.040" thick boards.

author: gonnafail
author_rank: Contributor
timestamp: December 01, 2010, 01:13:54 am
content: The molex connectors are meant to be used with ribbon cable and are not soldered directly to the board. You could solder the ribbon to the board or use two of these molex connectors to make a small patch cable and then use one of the receptacles soldered on your board. The samtec would be nice if it will mount onto standard thickness boards.

author: joelby
author_rank: Frequent Contributor
timestamp: December 01, 2010, 01:15:40 am
content: Quote from: allanw on December 01, 2010, 01:07:29 amYeah.. it's not supposed to be mounted to a board at allQuoteAh! Now I remember. The pins on the top and bottom will probably be flush with the PCB, so if your board is too thick it might not fit on the edge at all. You can usually get away with using a thinner board, but this is usually a bit ugly too and probably not acceptable for this sort of connector (I've done it with SMA end launch connectors and plenty of solder)

author: allanw
author_rank: Frequent Contributor
timestamp: December 01, 2010, 01:17:52 am
content: Unfortunately it probably won't fit.I'll try to kludge it anyway. Seems like the easiest and cheapest choice.Also, these cables aren't too expensive:http://cgi.ebay.com/1FT-ULTRA-VHDCI-SCSI-5-V-MINI-CENTRONICS-68-LVD-CABLE-/380283561946?pt=LH_DefaultDomain_0&hash=item588aaaa7da#ht_1332wt_905

author: joelby
author_rank: Frequent Contributor
timestamp: December 02, 2010, 05:18:45 am
content: Do you make the boards yourself or get someone to do them? 0.8 mm isn't too much more expensive than 1.6 mm from PCBCART, and the PulsarProFX system comes with 0.8 mm boards.I've almost convinced myself that I should just get a bunch of connectors from All Best. I'll theoretically need about 5, so this *nearly* works out cheaper than using the Samtec edge mount connector ($33 from element14). Would either of you, or anyone else, be interested in buying some? They'd probably work out to about $15 each + postage. The only annoying thing is that they have a 4-6 week lead time and I'd rather have something a little quicker than that. Given six weeks of thumb twiddling waiting for them (during which I'd miss my project deadline) I could probably get a good way toward designing my own FPGA board with the peripherals I want and wouldn't need any connectors at all.Using an eBay cable and a through-hole female connector works out to about $65 :-/

author: allanw
author_rank: Frequent Contributor
timestamp: December 02, 2010, 05:21:18 am
content: I believe you can buy the Samtec connectors directly from their website for $10 each. I ordered one as a sample.I didn't want to use 0.8mm boards because they're structurally pretty weak, but I guess that doesn't matter too much for something that''ll only be 2" by 2"

author: joelby
author_rank: Frequent Contributor
timestamp: December 02, 2010, 05:42:40 am
content: Yeah, I'll see if they'll send me some samples as well - hopefully sooner than 4-6 weeks

author: joelby
author_rank: Frequent Contributor
timestamp: December 07, 2010, 01:53:05 am
content: Good news - the Samtec connectors fit.The bad news - the data sheet is not so great! Pin alignment isn't described clearly. I thought that the pins were offset by half a pin spacing, but then I looked at the STEP model and they were paired vertically. As I'm in a bit of a rush, I foolishly ordered PCBs yesterday afternoon and the sample connectors arrived today. It looks like they're offset by an entire pin width.Hopefully it's not too late to get the PCB design changed without incurring the tooling cost again!Once the boards arrive and I've verified that it's okay, I'd be happy to share the library if anyone wants it. I've also made patterns for the Hirose FX2 and All Best male connectors, though these haven't been verified.

author: allanw
author_rank: Frequent Contributor
timestamp: December 09, 2010, 07:14:30 pm
content: Yeah I got the Samtec sample too. It definitely will not fit on a 63mil thick board. Also, the board must be less than 30mm wide to fit into the connector. Also I may be wrong about the location of the signal pairs. It's probably side-by-side, not on different layers.

author: joelby
author_rank: Frequent Contributor
timestamp: December 10, 2010, 01:51:39 am
content: Quote from: allanw on December 09, 2010, 07:14:30 pmI've just checked again with an ohmmeter and they're definitely on different layers.I also decided that they were offset by half a pin width rather than a full width. I'll be pretty gutted if it doesn't fit my PCB when it arrives!

author: fvnktion
author_rank: Newbie
timestamp: December 12, 2011, 09:15:56 pm
content: Just FYI, in regard to the VHDCI-CONNECTOR (mates to VHDCI connectors on Digilent boards).Now available at digilent store:http://digilentinc.com/Products/Catalog.cfm?NavPath=2,393&Cat=3search down the list for VHDCI-CONNECTOR.Also, the datasheet is here:http://www.digilentinc.com/Data/Documents/Product%20Documentation/R-HS-008068-2C_receptacle.pdf

author: mrflibble
author_rank: Super Contributor
timestamp: October 11, 2012, 03:16:13 pm
content: And for those of us in Europe:http://shop.trenz-electronic.de/catalog/product_info.php?manufacturers_id=16&products_id=924

author: DavidDLC
author_rank: Frequent Contributor
timestamp: October 11, 2012, 05:41:53 pm
content: Take a look to the Zedboard.http://zedboard.org/It is about the same price and it is newer.David.