How to interface digital output of FPGA to a DAC?

Question

I currently have a very, very basic DDS core(?) with a counter, tuning word, and sine LUT that outputs 16 bit values to correlate with a sin value for a DAC. I am using the Nexys 4 DDR board and my DAC is a peripheral module designed exclusively for FPGAs. If its a 16-bit DAC, why does it have 6 pins, only 4 of which are for data? And how should I send the binary information from my 16-bit generated sin value to the DAC in order for the DAC to do a successful conversion?

Here is my code (I know its rudimentary, please forgive the mistakes, I will work them out once I properly know how to interact with the DAC!)

module sin_LUT(
  input clk,
  input [0:3] M,
  input rst,
  output reg [16:0] data_out,
  output reg [32:0]test
);

//counter

//declaring constant
integer i;
integer int_M;

always @(M)
  int_M = M;

always @(posedge(clk))
begin
if (rst)
  i <= 0;
else if (i >= 29)
  i <= 0;
else
  i <= i + M;
end

//testing purposes
always @(i)
  test = i;

//sine LUT
always @(i) begin
  case (i)
    0: data_out = 16'D32768;
    1: data_out = 16'D39812;
    2: data_out = 16'D46526;
    3: data_out = 16'D52598;
    4: data_out = 16'D57742;
    5: data_out = 16'D61718;
    6: data_out = 16'D64341;
    7: data_out = 16'D65487;
    8: data_out = 16'D65103;
    9: data_out = 16'D63208;
    10: data_out = 16'D59889;
    11: data_out = 16'D55302;
    12: data_out = 16'D49661;
    13: data_out = 16'D43230;
    14: data_out = 16'D36310;
    15: data_out = 16'D29225;
    16: data_out = 16'D22305;
    17: data_out = 16'D15874;
    18: data_out = 16'D10233;
    19: data_out = 16'D5646;
    20: data_out = 16'D2327;
    21: data_out = 16'D432;
    22: data_out = 16'D48;
    23: data_out = 16'D1194;
    24: data_out = 16'D3817;
    25: data_out = 16'D7793;
    26: data_out = 16'D12937;
    27: data_out = 16'D19009;
    28: data_out = 16'D25723;
    29: data_out = 16'D32768;
    default: data_out = 16'b0000111100001111;
  endcase
end

endmodule

datenwolf · Accepted Answer · 2016-07-13T20:38:42.230

The datasheet for this DAC board says it uses an Analog Devices AD5541 DAC:

http://www.analog.com/en/products/digital-to-analog-converters/da-converters/ad5541a.html

The product page also has a link to the DAC datasheet. From this datasheet I pulled the following information: This thing uses a SPI interface. A select line (CS) which you pull low to indicate the DAC that you want to send it data. A data line (DIN) at which each single bit is presented. And a clock line (SCLK) that makes the DAC read a bit from the data line the moment it goes from low to high.

Here's the timing diagram

The LDAC input, if pulled low, tells the DAC to output with every update of the serial data register.

When developing electronics being able to source documentation and reading it is paramount. I've used a couple of different SPI DACs in various projects already, also some from AD. But not the AD5541 one. But the whole answer above I used information I got from reading the relevant datasheets for a couple of minutes. If programming FPGAs is your thing that you absolutely must cultivate the skill to do as such.

How to interface digital output of FPGA to a DAC?

1 Answers1