Distorted o/p in EXC_OUT Signal from EVAL-AD2S1210SDZ

Question

I am trying to use EVAL-AD2S1210SDZ to read the angle of a resolver. But when I checked the o/p Excitation signal in CRO, I am not getting a sine signal . I am getting a clamped distorted signal. 
 I am using the op-amp AD8397 with 0.866 gain. 
 Can someone please help me to understand why not getting the exact signal at output.

@skowalik · Accepted Answer

tpsamuel, 
 Can you please indicate what the position settings are for LK701 - LK703 and LK503? 
 Please also verify you see 12V at U4 and U9 pins 8. 
 Also can you please indicate what load you have connected to EXC and EXCB outputs at connector J6. 
 This information should be sufficient to let me know where the problem might be. 
 Sean

@skowalik · Answer

tpsamuel, 
 If i understand your query correctly you are asking if you can write to the register using another controller and remove the SDP control board. Is that correct? If so can you tell me which interface protocol you want to use (SPI/Parallel) and I can give you more specific directions. 
 In short however you can use connectors J3 and J4 to access most of he signals you need for the communication and then wire in whatever processor interface you desire. 
 If that is not the answer you were looking for then unfortunately there is no way to manually set the excitation frequency using pin selection. This functionality is available on the AD2S1205 but that device is fixed at 12-bit resolution. 
 Sean

@skowalik · Answer

tpsamuel, 
 First you'll need to change LK9 to position B to select the serial interface. 
 Next connect the following jumpers as follows to configure the interface for access through connector J4. 
 LK1: Position C (Gives Software Control to SAMPLEb on J4, Connect to I/O on Arduino Board) 
 LK2: Position B: Tie CS to ground to permanently enable AD2S1210 interface for this board. 
 
 OR Leave at Position C (Gives Software Control to CS on J4, Connect to I/O on Arduino Board) if you want to connect multiple instances to the same IO port. 
 
 LK3: Position B Tie RD to VDRIVE. 
 LK4: Position C (Gives Software Control to A0 on J4, Connect to I/O on Arduino Board) 
 LK5: Position C (Gives Software Control to A1 on J4, Connect to I/O on Arduino Board) 
 Configure LK6, LK7 to the desired RESOLUTION.... You will need to match this setting when programming the part in configuration mode. 
 Then connect arduino board as follows to the AD2S1210 EVB. 
 J4-1 (SAMPLE): GPIO for controlling sample 
 J4-2 (CS) If Connected GPIO for Controlling enable 
 J4-3: NO Connect 
 J4-4 (WR/FSYNC): Chip Select of SPI interface 
 J4-5, J4-7 - Ground 
 J4-6 - VDRIVE or Arduino VCC. 
 J4-8 (SDO): Connect to MISO of SPI Interface of Arduino Controller. 
 J4-9 (SDI): Connect to MOSI of SPI Interface of Arduino Controller. 
 J4-10(SCLK): Connect of SCLK of SPI Interface of Arduino 
 J4-11(A1) Connect to GPIO for controlling mode of operation 
 J4-12(A0) Connect to GPIO for controlling mode of operation 
 I would also construct your code to use SPI MODE 3. 
 Hope that get's you started. 
 Sean

@skowalik · Answer

tpsamuel, 
 What your are asking for is outside the scope of the support model for this forum. However I can in general tell you the steps you'll need to consider based on my experience with Arduino in the past. Please be sure to Verify you have enough I/O and resources on the NANO to do everything you need before making your purchase. 
 1) Include SPI.H header file 
 2) Define your pin connections using pinMode function. 
 3) Use the Arduino SPI commands to construct write and read access functions for configuration and normal mode access. I would recommend creating a variable called mySpiSettings of type SPISettings to pass to this function so you don't have to repeat it each time. With regard to this please use SPI_MODE1 as I believe I misspoke in my previous recommendation. 
 4) Setup a Timer to generate an interrupt at the rate you wish to execute normal mode position/velocity reads. 
 5) Setup your Main loop to do the following. 
 A) configure the AD2S1210 to your desired configuration. 
 B) Enable the timer and repeat for desired number of samples/forever 
 If (interrupt) 
 { 
 Read Measurement(s) 
 } 
 else 
 { 
 do nothing 
 } 
 
 Sean

@skowalik · Answer

tpsamuel, 
 For the parallel interface make the following changes to what I mentioned above. 
 
 LK9 - No change. Leave at position A for Parallel Mode. 
 LK3 - Move to Position C and drive RD with a GPIO from the Nano board 
 Move all connections for DATA I/O to J3. 
 J3-1 -> DB0 
 J3-16 -> DB15 
 All bit assignments for the databus (DB) are in ascending numerical order. 
 If you run short on I/O remember that you can access position and velocity measurements through configuration mode so you could use just DB0-> DB7 to get started. 
 Sean

@skowalik · Answer

tpsamuel, 
 The register map simply tells you which bits of the position/velocity register you are accessing when addressing register 0x80 or 0x81. If 0x80 you are effectively outputing POSITION[15:8] to DB7-> DB0; likewise addressing 0x81 you get POSITION[7:0] output on DB7-> D0. 
 
 Sean

@skowalik · Answer

tpsamuel, 
 No you'll need to strobe sample to pull the data from the loop output into the output register so you can access the data from the serial interface. 
 
 Sean