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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
RX_B.


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
http://www.semiconductors.philips.com/news/backgrounders/bg_esc9727/


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.


Eric




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