DAC81408EVM: DAC81408EVM

Hi Lap,

Welcome to the E2E forums!

I assume you are using your own SPI controller (rather than the USB2ANY), can you share a screenshot of the SPI transaction? Usually issues like this are due to a misformatted SPI frame.  Please confirm that your clock edges are correct.

In addition, you should note that this is a 24bit SPI packet, unless you have CRC enabled.

Thanks,

Paul

Hi Paul,

I am using the TI C2000 Delfino MCU F28379D LaunchPad™ development kit to generate the SPI signal. I can successfully

control the DAC80508EVM. However, once I changed to the DAC81408EVM, I cannot write to the configuration registers.

The following pictures depicts the two commands I sent through the SPI:

SpiaRegs.SPITXBUF = 0x8300;                         // read operation to SPICONFIG register (first access cycle)

SpiaRegs.SPITXBUF = 0x0000;                         // second half of the 32-bit data

while (SpiaRegs.SPIFFRX.bit.RXFFST != 2) {}  // two words has received -> done

*rr = SpiaRegs.SPIRXBUF;                                // removal of the 1st received words

*(rr+1) = SpiaRegs.SPIRXBUF;                         // removal of the 2nd received words

SpiaRegs.SPITXBUF = 0x8300;                       // read operation to SPICONFIG register (second access cycle)

SpiaRegs.SPITXBUF = 0x0000;                       // second half of the 32-bit data

while (SpiaRegs.SPIFFRX.bit.RXFFST != 2) {} // two words has received -> done

*rr = SpiaRegs.SPIRXBUF;                               // removal of the 1st received words

*(rr+1) = SpiaRegs.SPIRXBUF;                        // removal of the 2nd received words

The data I get back from the read operation (second access cycle) is 0x800AA483. The "0AA4" is the default data for the SPICONFIG register. One of

the problem is that I am expecting to get 0x830AA4XX instead of 0x800AA4XX (X: don't care). Another question is that I am using the 24-bit SPI access

but the LaunchPad kit only allows sending 16-bit data (am I right?). Therefore, I send two 16-bit data and the DAC should automatically ignore the last

8 bits of data.

Now, If I send the write operation 0x030A8400 to the DAC, the SPICONFIG register is still "0AA4" not "0A84". I am thinking this maybe the 24-bit/32-bit

access problem. Please help.

Thank you.

Lap

Hi Lap,

I suspect this is a 24/32bit access problem.  Can you try only sending 24bits? I am not 100% familiar on how to configure the MSP430 for this, but I suspect you can change the size of the TX buffer.  

In addition, you could verify the CS line as well. 

Thanks,
Paul

Hi Paul,

I have tried to sending only 24-bit data and I can now write to all registers except the DACn registers (address: 0x14 to 0x1B).

Therefore, I cannot get and analog output from the DAC. Is the addresses of the eight DAC registers right? (0x14 to 0x1B).

I don't understand why I can't write to these registers.

Regards,

Lap

Hi Paul,

Yes, I realized that the DAC registers are write only and I need to power up the DAC channels before using them.

It is working now. Thank you for your help.

Lap