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AD5421 SPI communication issues

Question asked by rafael on Sep 22, 2016
Latest reply on Oct 6, 2016 by rafael

Hello,

 

I am having trouble communicating with the AD5421 through SPI.  It seems like I am receiving back the exact same instruction I send to the slave device on every transmission (regardless of whether I am trying to read a register or give a write command) and it happens all in one command (as opposed to happening on the subsequent write command).

 

I am sending 32 bits of data with CRC as the last 8 bits.  My first command is to the control register: 0x02F820EC in which I disable the automatic feedback of the fault register.  When I send this, I receive the exact same message I just sent: 0x02F820EC.

 

I then send a command to read back the control register: 0x8200009C, to which I receive the reply: 0x8200009C.

 

Next, I send a command to the DAC register to output 16mA by sending: 0x01C0005B, and I just receive the exact same message back: 0x01C0005B.  If I measure the current it is held low at the fault value of 3.2mA.

 

Here is a picture of the scope

 

Thanks,

 

Rafael

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