Basys3 IO standard 1.8v

[rangaraj]

Hi,

 recently I bought basys3 board from diligent. In my project I need to use 3 GPIO's both input & Output at 1.8V.Kindly suggest me what I need to change?

As from the website , I know I need to change in the constraint file(XDC).bank 14 pins & set CFGBVS = GND.

https://www.xilinx.com/support/answers/57045.html

do I need to change anything in the board.

 

 

[D@n]

@rangaraj,

One of the great strengths of FPGA's is their ability to handle multiple voltage standards.  Indeed, they can be used as smart voltage translators.  From this standpoint, your request isn't all that uncommon.

What you are missing, though is that I/O voltages on FPGAs are set by bank, not by pin.  Further, the are set by the power supply voltage applied to the I/O bank in question.  To change the I/O voltages on a bank of Basys3 I/O pins, you would need to find the power supply pin for the bank, desolder it, route a new wire with the appropriate voltage on it to the pin, and solder that in place.  It's not a trivial change.

If you examine the Nexys Video board's schematic, you can see all of the work the Digilent engineers had to go through to make one bank have an adjustable voltage.  In particular, look at bank 15 on page 10, and bank 16 on page 11, and then the power selection logic at 4A on page 15.  The process was rather involved, and a lot of pins are affected.

The basys3 board's pins on the other hand are ... pretty well locked down to their particular voltage standards.  As a result, the easiest way to do what you wish to accomplish is to purchase a separate voltage shifter that you can plug into a PMod port.

Sorry this isn't the simple answer you were looking for,

Dan

[rangaraj]

Dear Dan,

 Thank you for the prompt reply. I understood that we need to change the Voltage in the Bank from the link https://www.xilinx.com/support/answers/57045.html .

But even I change in the constraint file still we need to change it in the Basys3 board. From your reply I understood that we need to desolder it & solder it to appropriate wire. I went through the schematic I didn't find any 1.8v but we have 2.5v , 3.3v & 1.5v. So I need to give external voltage of 1.8V ? if so which wire I need to desolder in bank 14 or bank 15. will you please point it to me ?

 

Regarding the level shifter, if I am not wrong its a bidirectional levelshitfer (1.8v to 3.3v & 3.3v to 1.8v) am I right ?

kindly advise.

Thanks and Regards

Lakshman.

 

 

[D@n]

@rangaraj,

At this point, you are asking questions beyond my own level of understanding.  I'd have to go back to the Xilinx doc's for the part and dig that information out of them.

Perhaps someone else on the forum, @jpeyron perhaps?, has a better answer for you.

Sorry,

Dan

[Bianca]

Hi @rangaraj,

Basys 3 has indeed a 1.8V power supply. You can find it on the schematics on the last page: https://reference.digilentinc.com/_media/reference/programmable-logic/basys-3/basys-3_sch.pdf and you the 7th sheet you can see the powerbank that uses that voltage. You can output the 1.8V from the board, although it depends on the power you need. The 1.8 can output 300mA. The supply is curently used just for the FPGA If you look closely on the schematic on the last page you can see W1 W2 and W3. on W2 you have a 1.8V PS You can find on the TOP just above the Basys3 label a big plated hole. From that point you can draw 1.8V. You can also fint the 3.3 and the 1.0 and W1 and W3 marked on the bottom.

I hope this helps.

Best regards,

Bianca

[rangaraj]

Dear Dan & Bianca,

 Thanks for showing the place in schematic. I see that LED , SwBttons & VGA are connected to the same bank. If I change the voltage to 1.8v for bank 14 ,then the other LEDs, VGA's will work ??

Having second thought to use the level shifter as suggested by dan, is that level shifter is bidirectional ?

http://store.digilentinc.com/pmod-lvlshft-logic-level-shifter/

 

kindly advise.

Thanks and Regards

Lakshman.

[D@n]

@rangaraj,

I would be very surprised if the other peripherals on that bank continued to work.

As for the level shifter, judging by the sell page, the directions of the various pins are controlled by physical switches.  A quick check of the first page of the data sheet for the underlying part confirms this.  So ... you should be able to use these pins for both input and output, but you'll need to flip the appropriate switch when you wish to switch direction.  Hence, it would make the most sense to change direction with separate configuration files.  Do you need a real-time ability to switch the direction of the various wires?

Dan

[lakshman]

Dear Dan

Thanks for the info. Yes I do but I can use 2 pins to combine & do the job. (input one pin 1.8v to 3.v & output one pin 3.3 v to 1.8v -->combine the output pin to the input. IF input working then output in high impedence state & out put is sending data then input is in High impedence state).

Correct me if I am wrong.

Thanks and Regards

Lakshman.

[D@n]

@lakshman,

The key question is whether or not the high impedence state will go through the voltage translator and create a high impedence state on the other side?  Reading through the spec sheet, I can't convince myself that it will do that.

The last time I had to do this, I was working with SDIO commands from a CPU going through an FPGA to an SD card.  In that case, we used wires from the CPU to tell the FPGA which direction it's voltage translation should operate in.  You might find, then, that you need to create your own voltage translator board and use one pin for the I/O pin, and a second pin to indicate to the voltage translation chip which direction it should do it's translation in.

Dan

[rangaraj]

Thank you Dan.

 

Thanks and Regards

Lakshman.