DAC8750: SPI communication, daisy chain configuration

TISL

Expert 4105 points

Part Number: DAC8750

Dear e2e support,

My customer try to communicate with two DAC in daisy chain, but do not have answer on SDO.

The clock frequency is at 252KHz. The signal bus level has been measured at 3.3V.

Here is the sequence used to get the status of the 2 devices :

CLR low

Latch low

Send 0x020000020000 => 2 x 24 bits

Latch high

Wait 10 us

Latch low

Send 0x000000000000 => 2 x 24 bits

Latch high

schematic used:

Would you have any idea where to investigate?

Regards,

over 4 years ago

0 Reza Abdullah over 4 years ago

TI__Intellectual 1570 points

Hello,

On the DAC8750, daisy chain is disabled at startup. The customer has to first enable it for the devices in the daisy chain to use it. This is done by writing '1' to the DCEN bit of the control register (addr 0x55, bit 3).

Regards

Reza

0 Christophe LACOIN over 4 years ago in reply to Reza Abdullah

Prodigy 60 points

Hi,

I see this bit, but i'nt undestand if this bit must be set for the 2 DAC8750, or only the first.

when i send this data, i'll send 3 bytes or 6 bytes with correct data for the 2 DAC8750 ?

Rgds

Christophe

0 Reza Abdullah over 4 years ago in reply to Christophe LACOIN

TI__Intellectual 1570 points

Hello Christophe,

The DCEN bit must be set for all devices in the daisy chain. Can you send me an example of what command you want to send so I can explain to you how to send the data to the devices? Thanks.

Regards

Reza

0 Christophe LACOIN over 4 years ago in reply to Reza Abdullah

Prodigy 60 points

Hello,

I send

CLR low

Wait 10 us

// send control

Latch low

Send 55100D55100D=> 2 x 24 bits (ADD_WR_CTRL)(8bits) (CTRL_OUTEN | CTRL_DCEN | CTRL_RANGE_4_20MA)(16 bits)

Latch high

Wait 10 us

// read Status

Latch low

Send 020000020000=> 2 x 24 bits (ADD_RD_REG)(8bits) (ADD_RD_FCT_STATUS)(16 bits)

Latch high

Wait 10 us

// read data

Latch low

Send 000000000000=> 2 x 24 bits

Latch high

I receive: 000000000000

Regards

Christophe

0 Reza Abdullah over 4 years ago in reply to Christophe LACOIN

TI__Intellectual 1570 points

Christophe,

The routine looks good to me. Are you expecting some error in the status register? If not, then you should expect to readback all zeroes. Have you tried reading back another register, like the control register.

If that doesn't work, can you try first enabling daisy chain on the first device (Latch Low 24 bits DCEN cmd, Latch high). Then enable daisy chain on the 2nd device after wards and repeat the other steps of your procedure. This would ensure that both devices are enabled before you readback the status register.

Regards,

Reza

0 Reza Abdullah over 4 years ago in reply to Reza Abdullah

TI__Intellectual 1570 points

Hello Christophe,

Do you have any update on this issue? Are you now able to communicate in daisy chain mode?

Regards

Reza

0 Christophe LACOIN over 4 years ago in reply to Reza Abdullah

Prodigy 60 points

Hello Reza.

Yes, i'm communicate in daisy chain mode.

My first problem is address are in decimal (my PC has freeze and my address corrections losted).

2nd, i send now the DCEN to the first chip, and in a second sequence, i send DCEN to second chip.

and now, it's OK

Rgds

0 Reza Abdullah over 4 years ago in reply to Christophe LACOIN

TI__Intellectual 1570 points

Thanks for the update Christope. I'm glad it is now working. Can you please close the thread then?

Regards,

Reza

0 Christophe LACOIN over 4 years ago in reply to Reza Abdullah

Prodigy 60 points

OK, but how i close this thread ? I see any button or somethink else to close this trhead.

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DAC8750: SPI communication, daisy chain configuration