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ADE7753 and STM32 - based Power Meter

Question asked by TrendChaser89 on Sep 27, 2012
Latest reply on Sep 30, 2012 by TrendChaser89

I am currently working on a digital meter with ADE7753 and STM32 MCU.  I had my schematic based on AN564 reference design and ADE7753 Evaluation Board.  I tested the SPI interface between these devices and noticed that the DOUT pin of ADE7753 responded to the command byte sent by the MCU.  The command byte is a read command to the SAGCYC register whose default value is 0xFF.  Signal from the DOUT pin went high for 8 clock cycles representing 0xFF.  However, it does not go back to its low state right away (see attached image).  It seems to behave like a discharging capacitor.  What could have caused this strange behavior?  I placed a pull down resistor on the line connecting ADE7753's DOUT and MCU's MISO.  Is this okay? Would it affect the performance of the device? The MCU could read 0xFF from the SAGCYC register and other default values from the registers of ADE7753 when I placed the resistor. I'm a newbie to electronics, microcontrollers, metering ic's, programming.  Appreciate your help a lot.