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Continuous Read on AD7793

Question asked by Aitortxo on Mar 19, 2012
Latest reply on Jun 15, 2012 by MaryMc

Hello,

 

I have an 'Eval-AD7793' board and trying to interact through SPI interface.

 

After configuring the channel, callibrated zero and full scale, and set mode to continuous conversion, single reads sequences are executed perfectly (as in figure18, AD7793 DataSheet):

 

Send 8 CLKs: 0x58 [Read operation for Data Register]

Send 24 CLKs: 0xFFFFFF [Generate 24 CLKs to let AD7793 set current Data Register value]

 

This process of reading values is the one implemented in AD7793 Evaluation Software

 

What I need is the process described in figure 19, AD7793 DataSheet: Continuous Read

 

When sending 8 CLKs: 0x5C [Continuous Read operation for Data Register]

 

I see DOUT/RDYn signal going high and low (high for 800us, as stated in http://ez.analog.com/message/23813#23813)

 

--- Attatched capture trigger point (see below) ---

 

When sending 24CLKs: 0xFFFFFF [Generate 24 CLKs to let AD7793 set current Data Register value]

The first conversion is correct

But next conversions (started on falling edge of DOUT/RDYn) don't show similar values to first one.

The second conversion has 8 CLKs with '1's and '0's and the rest 16 CLKs  all '1's.

The rest of conversions have a first part of all '0's and a second part of all '1's...

Attatched is a capture of signals:

CSn

DOUT/RDYn

SCLK

before sending the first 24CLK block (as noted before)

 

Each vertical black line separates a consecutive capture

Trigger fires on Rise edge of SCLK

SCLK is about 520kHz, 50% duty

 

Please, can you help me find a clue to make continuous read work?

 

Thanks in advance,

Aitortxo.

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