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Spartan-3E Slave Serial Configuration

Hi All,

I'm designing a circuit for configuring 4 Spartan-3E FPGA from an Atmel AVR microcontroller.

I want to configure the FPGA in slave serial mode. Because of the difference in the supply voltages, there are some different logic voltages, some 2.5V, some 3.3V

AVR 3.3V FPGA VCC0 3.3V FPGA VCCAUX 2.5V

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Xapp453 states that CCLK needs to be driven with 2.5V logic, however, the Spartan-3E datasheet states (Page 68) that CCLK is powered by VCC0_2 which will be 3.3V.

I'm guessing that the contradiction is due to XAPP453 being for Spartan-3, not Spartan-3E.

I just need to know if CCLK needs the logic level changing as well the PROG_B signal.

Could someone just check the following for me:

PROG_B driven by AVR needs to be 2.5V logic DIN driven by AVR 3.3V logic (I think) CCLK driven by AVR 3.3V logic

INIT_B driven by FPGA 3.3V logic DONE driven by FPGA 2.5V logic DOUT driven by FPGA 3.3V logic

Many thanks Andy

Reply to
Andrew Greensted
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Hi Andy, That's what I did on my last S3E design. I pulled PROG_B low through a schottky diode with a pullup to 2.5V at the FPGA. All that said, I would rely on the datasheet more than usenet! HTH, Syms.

Reply to
Symon

Symon wrote: > Hi Andy,

Cheers Symon, My plan was to use one of those tiny-logic single gates, they've got 5V tolerant inputs and can be by 2.5V. That should do the level conversion nicely. Andy

--
Dr. Andrew Greensted      Department of Electronics
Bio-Inspired Engineering  University of York, YO10 5DD, UK

Tel: +44(0)1904 432828    Mailto: ajg112@ohm.york.ac.uk
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Reply to
Andrew Greensted

Have a look at pages 101-121 of:

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This info may have all percolated into the datasheet by now, but that's still a most useful document.

Brian

Reply to
Brian Davis

That's good. Use a dual schmitt trigger, and clean up CCLK while you're there. Ringing on CCLK can be a real nuisance.

John

Reply to
John Larkin

Ahh yes, I th> That's good. Use a dual schmitt trigger, and clean up CCLK while

Good plan.

Thanks both Andy

Reply to
Andy

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