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Interfacing ADS8556 with 320TMS6713

rohith mohan
Prodigy 100 points

Other Parts Discussed in Thread: ADS8556

Hi,

I was trying to interface the ADC 8556 along with the DSP c6713 processor.

Have been trying to achieve it with the kits ADS8556EVM and 6713 DSK.

The main specifications which I am looking at is :

> Serial Communication.

> Interface via McASP [ My McBSP is already taken up by other pheripherals ].

 

Connections done are [ McASP - ADS8556 ]: 

-> AFSX1 -----------------  CONVST_A & CONVST_B & CONVST_C [ Since I want all 6 channels to be triggered at the same time]

-> AFSR1 ----------------- FS/CS

-> ACLKX1 --------------- SCLK

-> AXR1[0] ---------------  SDO_A   [ SDO_B & SDO_C are grounded. sel A = Vdd,  selB = selC = gnd ] 

-> AXR1[4] --------------- SDI 

 

I am making the ADC work in HW mode [ planning to convert it to software mode on success of HW mode ].

All recommended settings suggested in the technical datasheet of 8556EVM for HW serial mode has been made. 

From the DSP, I am planning to generate a pulse of width greater than 3uS for the CONVST signals [ as I am not planning to use the busy signal].

I am generating a CLK of period 1uS.

 

Now , the problem is that -  1) When I set the CONVST signal high , the busy signal of 8556 is not going high.

2)I am not sure why I am not able to get the serial data out of SDO.

I am not able to infer whether there is a problem in my approach.  

Please guide me with the same. 

  • TI__Guru**** 183271 points

    Hi Rohith,

    The default state of the ADS8556 board is for the STBY signal to be active, this could be part of your problem.  Please insert a shunt jumper across pins 7-8 of J4 on the EVM, this will set STBY high.   I would also suggest that you pulse RESET high after power up.  This pin is pulled low via R39 at J1 (pin 1) on the EVM.  You could use perhaps one of the DC_CNTL lines from the TMS320C6713 DSK to accomplish that.

  • in reply to Tom Hendrick
    Prodigy 100 points

    Hey. 

    Thanks for the reply.

    I have another basic problem. 

    The first ADC EVM I ordered had a pin short between +VA and -VA [ I guess due to a surge ].

    So I ordered the another ADC 8556 EVM. This time I made sure that all my supplies are fine and connected.  It was fine for 2 weeks. With the same connections, this time I have a short between DVdd and ground. I have even connected BVdd to DVdd via JP4.

    Since 2 boards have been spoiled, I still do not know what the problem is. Is there a way to fix it [ I mean if this is a common problem ]. I have tried removing the capacitors and rechecking the connections too. It was still shorted.

     

    Thank you. 

     

  • in reply to rohith mohan
    TI__Guru**** 183271 points

    Hi Rohith,

    Sorry to hear that you've had problems with the ADS8556EVM!  I've not heard of any similar issues with the board itself, so please try to give me a few details about how you are applying power, what signals do you have on the inputs etc.  What sort of controller are you connected to?  What is your analog input source? How are the grounds between your controller and the EVM as well as the analog inputs and the EVM wired?

  • in reply to Tom Hendrick
    Prodigy 100 points

    1) How you are applying power ?

    For J3 on EVM.

    1 -> +12V

    2 -> -12V

    3 -> +5V

    4 -> -5V

    5 -> GND

    10 -> +5V    [ JP4 connected towards 5V side ] [ The middle pin of JP4 is the on which has got shorted to GND. ]

     

    2) What signals do you have on the inputs 

    Input J2.1 -> gnd of signal generator.

    J2.2           -> 2.5V from signal generator.

     

    What sort of controller are you connected to?  What is your analog input source? 

    I have not connected it to any controller. I was trying to observe only the busy signal.

     

    How are the grounds between your controller and the EVM as well as the analog inputs and the EVM wired?

    Only the power grounds were connected to AGND. 

  • in reply to rohith mohan
    TI__Guru**** 183271 points

    Rohith,

    The only thing between pin 2 of JP4 and GND is a ferrite bead and two ceramic capacitors.  For chip capacitors, one of the most common failure modes is low resistance, often from mechanical damage, usually induced during manufacturing.  I'll contact you off line to see how we can arrange to swap boards (a good one from me for a bad one from you) as I would like to see if there is something we need to address on the EVM production line.

  • in reply to Tom Hendrick
    Prodigy 100 points

    Sure.

    That sounds good. Thank you !

    You can contact me at rmohan2 'at' ncsu.edu