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Question

Howdy,

 

I'm looking for a device that can read a 5 Mbit NRZ pseudorandom digital stream (pn15) and stream it via USB in real time.

I've thought of using a standard serial to USB converter, but I don't think it would work because there are no sync bits.

I think the only way to really capture the bits would be to over-sample (>10 MS/sec) and then fit a clock to the serial signal.

I'm sure the Analog Discovery could do this with its 100MS/sec sample rate, but I'm looking for something that could stream it in real time.  I think I've read that the real time limit is 1-2 MS/sec, but I'm wondering if it would be faster since I'd only have to stream digital samples.

I'm willing to write some code if the functionality is exposed in the API.

Any information would be greatly appreciated.

 

Thanks,

Sam

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Hi @Sam Carey,

Welcome to the forums! I moved your forum thread to a better section where more experience engineers dealing with the Analog Discovery and WaveForms SDK will see your post.

thank you,

Jon

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Hi,

the MPSSE mode of a FTDI chip in the JTAG adapter will do the trick. It can do SPI-like full-duplex up to 30 MBits/second. There is a clock signal so the data signal can be anything.
Accessing that is a bit tricky (it goes via JTAG's USERx opcode) but the easiest option might be to connect an external FTDI chip SPI-style (transmit, receive, clock, some chip select signal for simple sync).

I'm heavily using the "SPI" via JTAG option myself, but it's a bigger project to make that work. A basic MPSSE driver for the FTDI chip (not JTAG but direct connection) can be done in a day or two.

If interested, check out FTDI's application notes on MPSSE and SPI. I wouldn't touch their JTAG example code...

Edited by xc6lx45

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