Compiler/DAC7750: DAC7750 write register

	dacValue = 4095; //test value
	DAC7750_SetOutValue (dacValue);
    ......
}

The purpose here is to set a DAC code on DAC7750 and reading voltage output from SDO. But whichever DAC value of code I write in my program I always get 0 V reading from SDO of the DAC7750 chip. Below is the main part that sets dacValue 4095 for the 12 bit DAC7750. I have attached the DAC7750.c (function implementations for DAC write register, configurations), DAC7750.h (register addresses defines), spi.c and spi.h (SPI library used to communicate on Raspberry PI).

DAC7750_SetOutValue (dacValue);

Please let me know why I am getting 0 V reading from SDO of the DAC7750 chip and help me in resolving the errors that might be causing this.

Jubayer,

Reza or I will provide you with an update by tomorrow. In the meanwhile, it would be helpful to expedite this to actually see the transactions on the SPI bus instead of reading code. Even if the code is perfect - there is still the possibility for a board-level analog problem which we would not detect from reading code.

Hello Jubayer,

Are you able to successfully read back data from any other registers? As an example, can you read back the data from the control register (addr 0x55) to confirm the correct setup of the DAC?

Also, what is the status of the CLR pin on your board?

Regards,

Reza

When I read from the control register (addr 0x55) the read back data is: 0xdc (220 in decimal)

CLR pin is connected to ground with 10k resistor, so it's always connected to ground GND.

Additionally, status register is also sending back 0xdc (220 in decimal).

I have also attached the diagram of circuitry.

I have attached the waveforms for clock (SCLK), DIN and LATCH (CS1/DAC1 for my example, as we are using a multiplexer to select which DAC to write to out of 12 DACs).

1. The yellow waveform ====  clock CLK

2. Blue waveform ==== data in (DIN)

3. Purple waveform ==== LATCH (Chip select CS1 in my example)

I have fixed the SPI frame implementation in the code, now it seems working. For the DAC value of 0x0000 I get 4 mA and DAC value of 0xFFF0 I get 20 mA. I also get status register value as 0.

I have attached the SPI transactions below:

Great! Are you also now able to read back the data from the registers? Please note that reading back the SPI registers requires two SPI frames. The first frame specifies the read command and which register to read. The second command is a NOOP and the data is clocked out of the SDO pin during the NOOP frame. 

Regards,

Reza