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Re: [Discuss-gnuradio] FrontEnd4702 take 29

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] FrontEnd4702 take 29
Date: Wed, 25 Feb 2004 11:14:24 -0800
User-agent: Mutt/1.4.1i

On Wed, Feb 25, 2004 at 10:04:28AM -0800, Matt Ettus wrote:
> Quoting Eric Blossom <address@hidden>:
> > This still leaves a snafu regarding using the aux_DAC outputs for AGC,
> > since there aren't enough of them for each card to have it's own, let
> > alone two.
> No it doesn't.  Each TX/RX pair gets 4 shared DAC outputs.  There are 8 total
> DAC outputs on the board, 4 for each TX/RX pair.  So using 2 for an RX board 
> is
> fine.

OK, Matt has set me straight on the aux_DAC and aux_ADC issue.
We've also found a solution for handling I2C at both 3.3V and 5V

Here's the summary:

There are four daughterboard slots.  Call them TX_A, RX_A and TX_B and
RX_B.  Transmit daughterboards will mechanically fit only into TX_A or
TX_B. Receive daughterboards will mechanically fit only into RX_A or

AUX_DAC usage:

There are a total of 8 aux DACs available on the motherboard.

The 8 aux DACs are split 4 to (TX_A and RX_A) and 4 to
(TX_B and RX_B).

To avoid chaos, for single wide cards we use the following convention:
RX boards may use AUX_DAC_A and AUX_DAC_B.
TX boards may use AUX_DAC_C and AUX_DAC_D.

If you are building a double wide TX/RX daughterboard
you may use all 4 aux DACs as you please.

[Electrical note: AUX_DAC_D, really the SIGDELT output of the AD9862,
 requires additional low pass filtering on any card that uses it.]

AUX_ADC usage:

There are 8 AUX_ADCs on the motherboard.  Each daughter board
gets two of them, not shared with any other board.  No problem.

3.3V and 5V I2C usage:

The motherboard runs the I2C bus at 3.3V.  Any daughterboard that
requires 5V I2C should use the bidirectional level shifter shown at

4702 I2C Whackiness

The 4702 can decode at 4 different addresses, but does it though one
pin.  Matt will work up a simple circuit that uses the I2C_A0 and A1
bits as input and drives the magic pin correctly.  This will ensure
that the 4702 board needs no jumpers and will perform properly in any
RX slot.


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