DAC7728: Power-up problem

Blue color: DVDD/IOVDD

Green:  AVDD

pink: REFA/REFB of first DAC

yellow:: REFA/REFB of second dac 

Note: pink and yellow trace is same

DAC1 not working, DAC2:working

Start-up:

Power-down

Power-down zoom

Thanks

I have 2 board: on which the 2 DAC and on other with a microcontroller (LPC1778).

I see,3 day of which follow each other, the morning i don't have any problem, and the afternoon the first DAC don't working.

The difference, is the temperature, more hot the afternoon.

I have refresh my DAC board, no change, i refresh my micro board, the first dac is work.
I change in loop the value of the dac for testing, and i heat my micro board, the DAC stop to change.
I attach the scop of data communication,
For send data to dac, i use 2 times (8bits bus).
First time set address and high data bit, and latch it,
Second time send 8 last bit data and unlock addresses and data
In the second time 12 bits data and 5 bits address is send to DAC

On the scop, the interest time for the DAC is when the pink trace is low (CS_dac), the value send is 2051 adress is 8 .

My RD/WR is all the time low except when we read.

The good:

The bad:

Thanks

Hello,

In page 12 of datasheet of DAC7728, this is not very clear:
The read operation is in falling edge of CS and data is valid on rising edge of CS.

And write operation 1, write is validated at falling edge of CS, but why we have the t2 and t4 time?

Thanks