Digilent Basys2

Digilent, Inc partners with Xilinx and designs and markets a range of FPGA development boards. The Basys2 is their entry level board, targeted at the education market with phrases like "Build digital circuits for less than the price of a textbook!" in their marketing. They offer pretty sharp Academic and US Student discounts, but there are quite a few hoops to jump through to qualify.

 

As the Basys2 has been used as the platform for course materials and textbooks, Digilent have far less freedom to add new features to the board-- for example, it still has a PS/2 port when no current PC ships with a PS/2 keyboard. Diligent also has an equivalent to Gadget Factory’s Wing system called PMOD.

The Basys2 comes in a DVD sized plastic case with foam padding, and includes a USB cable. One feature of the Basys2 that is either a help or a hindrance, is that all externally available signals from the FPGA have resistors in series. This aids with ESD protection and helps to prevent damage from abuse in the classroom environment, but can sometimes cause interfacing issues.

In my view the biggest flaw in the board is that Digilent have opted not to use a crystal to generate a stable on-board clock-- possibly to save cost (or maybe to remain compatible with the original Basys). The jitter present in its cheaper clock makes the Basys2 unsuitable for generating higher frequency signals-- for example, the VGA output is unusable for anything serious and most LCD monitors are unable to even sync with it! There is a socket for a second clock signal, although the required part is expensive and hard to source.

Note

The part number in the BASYS2 reference manual is wrong-- order something like SGR-8002DC-PCC-ND from Digi-Key to provide a stable clock, should you require one.

As I’m in New Zealand, I ordered mine from their ANZ distributor-- Black Box Consulting. They normally have everything in stock, so not only is it quicker than ordering from Digilent, the international shipping direct from Digilent is really, really, really expensive. Why is it you can get a Papilio FPGA board from Seeed Studios for US$49.90 including postage, but it costs US$36.66 to ship a $99 order from Digilent? Black Box Consulting charged me a reasonable AU$10.00 for shipping. 

 A quick comparison

Introducing the Spartan 3E FPGA and VHDL

                                                     Papilio One + LogicStart               Digilent Basys-250

FPGA                                                   Spartan 3E                                     Spartan 3E

Effective Gate Count                              250,000 or 500,000                         100,000 or 250,000

Programming interface                            USB                                              USB

Configuration ROM                                 Yes                                                Yes

VGA Connector and colour depth             Yes, 8 bit                                        Yes, 8 bit

Four digit, Seven Segment display           Yes, slightly bigger                          Yes

Host communication interface                  Serial over USB                              8 bit parallel (EPP)

Maximum host transfer rate                     300kB/s                                         170kB/s

LEDs                                                     8                                                    8

Slide switches                                        8                                                    8

Push buttons                                          1 (on joystick)                                 4, in a row

Mini-joystick                                           Yes                                                 No

PS/2 port                                                No                                                  Yes

On-board clock                                       32MHz, stable                                  25/50/100MHz, jittery

Carry case                                              No                                                  Yes

Analogue to digital converter                    eight 12-bit                                      channels No

Audio output                                           Yes, mono                                       No

Additional power connector                       Barrel jack                                      Two pin header

ESD protection on all connectors              No                                                  Yes

Size                                                       Smaller, thicker                                Larger

Open design                                           Yes                                                 No

USB cable supplied                                 No                                                  Yes

Add-on modules available                        Yes (remove LogicStart)                    Yes

Maximum user I/O pins                            48 (remove LogicStart)                     12 + 2 on PS/2

Voltages available to add-ons                   2.5V, 3.3V, 5V                                  3.3V

Soldering required                                   Yes, to attach headers                       No

Designed to work with Arduino S/W          Yes                                                   No

Has geek factor?                                     Yes, very underground                       No, used in colleges