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Cannot read device ID from AMC7812

irmus
Prodigy 80 points
Other Parts Discussed in Thread: AMC7812

Hi.

I have a problem to interface with AMC7812.

AMC7812 is connected with STM32 MCU with SPI interface.

First of all, I want to read Device ID register(0x6C). which is read-only and reset value of 0x1220.

After 100ms after power on, I made a 24 bit READ sequence(0xEC-0x00-0x00) on SDI and repeated it for every 500ms.

Returning SDO looks like some random values.

Attached images are captured SPI signal. 

Ch1 - nCS, Ch2 - SCLK, Ch3 - SDO(MISO), Ch4 - SDI(MOSI)

I can see 3 types of SDO sequence. But the value sets are changing over power cycle.

Here is SCH I made.

In the SCH, AVDD/DVDD is 5V, but attached scope images are with 3.3V AVDD/DVDD. Result is same.

Can anybody advise me?

Best Regards,

Hyunwoo Park.

  • 0
    TI__Genius 11750 points
    Howdy Hyunwoo,

    Thank you for the information. I've inspected your circuit and everything seems to be fine. As you mentioned above, the SPI reading seems to be incorrect, the register information reported on the SDO line doesn't align with the register address you are reading from -- these should be reporting the same value during correct operation. For example, you are trying to read from (0xEC), but SDO is reporting from (0x74), (0xF6). Can you provide the following timing characteristics below?

    1. SCLK falling edge to CS rising edge, or t7 timing parameter in Data Sheet
    2. State of Reset Pin, DVDD/AVDD supply, and IOVDD (oscilloscope capture)

    Best Regards,
    Matt
  • 0 in reply to Matthew Sauceda
    Prodigy 80 points

    Hello Matt.

    1. t7 is about 1.4us. But even I put some delay into t7, nothing changed.

    2. Here I attach a reset circuit schematic. Reset is steady high. 12V/DVDD/AVDD/IOVDD shows clean line on scope.

    But while inspecting power rails, I found SPI singals have many glitches. My board is configured with two PCBs, and SPI signal wire connects between them and I tested with too long wire so SPI signals crosstalked with them. After I change the cable with short one it can read stably.

    Thank you very much Matt.

  • 0 in reply to irmus
    TI__Genius 11750 points

    Hi Hyunwoo,

    I'm glad you were able to solve the problem.  

    Best Regards,

    Matt