How to easily extend the capacity of the Arty dev board to a solderless breadboard via the Pmod connectors...

[jdb2]

Hello. I recently bought a Digilent Arty FPGA dev board. I need to connect some 8-bit or 16-bit SRAM chips to the board and I have to determine what the best method would be, to bring out the ( 40, I believe ) data lines on the four 6x2-pin Pmod connectors on the side of the Arty and connect them to a solderless breadboard, preferably without any soldering involved in this process at all.

I need access to the Arty's LEDs and buttons on the top so I don't really want to go with a stackable Arduino shield, which requires much soldering to attach a solderless breadboard, at least, soldering is required for the Arduino shields that I've seen. Well, after thinking about my problem and the requirements for the SRAM chips in my design, I thought of a way to easily connect my Arty to any old breadboard. I plan on buying a few Pmod extender cables, some Pmod 2x6 pin headers / gender-changers and some 12-pin Pmod to DIP adapters. I could plug two or three Pmod extension cables into my Arty, plug 6x2-pin DIP connectors onto the ends of the cables and then plug the cables into a breadboard of my choice. I've made up a list of things I'd need to buy from Digilent and I think that I need a few of these : http://store.digilentinc.com/2x6-pin-cable/ , this : http://store.digilentinc.com/2x6-pin-header-5-pack/ , a few of these : http://store.digilentinc.com/pmod-dip-dip-to-12-pin-pmod-adapter/ and finally just any solderless breadboard.

 

I'm wondering if this is the easiest method with which one access all of the data GPIO lines exported by the FPGA via my Arty's Pmod connectors -- if I've missed something obvious or this question seems stupid, then please forgive me.

 

Any suggestions or advice would be appreciated,

Thanks,

jdb2

[sbobrowicz]

hey jdb2, welcome to the forum!

Your idea will work for getting all of the Pmod IO to a breadboard, but you could save a little money using these cables instead:

4x - http://store.digilentinc.com/2x6-pin-to-dual-6-pin-cable/

2x - http://store.digilentinc.com/6-pin-header-gender-changer-5-pack/

No Pmod DIP required because the 1x6 headers can plug directly into most breadboards (;

One thing you need to be aware of though, each 2x6 pmod only has 8 pins connected to the FPGA (along with 2 GND's and 2 VCC3V3's). That means your current plan currently nets you 32 I/O on the breadboard.

If you need more I/O than that, then I would use a similar approach with the shield header. It is possible to get 49 FPGA connected I/O off of the shield connector. some are more convenient to reach than others, so you may need to get creative with your cabling here. We have all sorts of MTE cables (1x1, 1x2, 1x4, etc) that might come in handy, you can check them out here:

http://store.digilentinc.com/all-products/accessories/connectors-and-cables/

A big question here is how fast is the SRAM going to be operating, and is it sync or async. 20 MHz tends to be a rough estimate of what switching speeds you can achieve with the standard pmods that have the 200 Ohms series resistors loaded (JA and JD on Arty). The "high speed" pmods (JB and JC on the Arty) don't have the series resistors loaded and should be able to switch as fast as you would need them to. Keep in mind the breadboard will further limit your speeds too.

Another potential gotcha: Make sure your SRAMs use 3.3V signaling, that is all that the Arty supports.

You know, it might be easier to use the DDR3 on the board, unless you have specific bandwidth and latency requirements. I suppose the other reason you might choose SRAMs is for the easier interface, but you could always port the sram2ddr HDL component from the Nexys4DDR to Arty and use that. It lets you access the 256MB DDR via a very wide, standard SRAM interface. Downside is that it has much higher latency and access times than your standard SRAM. You can find it here:

https://reference.digilentinc.com/learn/programmable-logic/tutorials/nexys-4-ddr-sram-to-ddr-component/start