|Subject:||Re: [Discuss-gnuradio] usrp_sink_s and other quick questions|
|Date:||Tue, 22 May 2007 12:06:44 -0400|
On Mon, May 21, 2007 at 04:19:58PM -0400, Steven Clark wrote:
> If I need pin-level access to the DAC chip, sink_s is my only option AFAIK.
> I understand that it's interleaved I&Q, don't worry about that.
> My original questions remain.
> On 5/21/07, Eric Blossom <address@hidden> wrote:
> >On Mon, May 21, 2007 at 10:48:04AM -0400, Steven Clark wrote:
> >> Hi all-
> >> Several quick questions.
> >> 1) For usrp sink_s, which bit of the short activates the MSB of the DAC
> >> chip? I.e., if I send 0bABCDEFGH IJKLMNOP, where each letter is either a
> >> or a 0, which letter matches the MSB?
What you sent to sink_s doesn't go directly to the DACs, but rather is
first interpolated and possibly upconverted.
The DACs run at a constant 128 MS/s. They are fed from the FPGA at
32 MS/s, and are interpolated by a factor of 4 in the AD9862. See the
AD9862 datasheet for details.
The I & Q data written to sink_s should be 16-bit 2's-complement
host-endian data in the range -32768 to 32767. The max and minimum
values that make sense actually depend somewhat on the associated RF
daughterboard. Analog clipping may occur at values smaller in
magnitude than +/- 32,767.
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