we are experiencing some problems with SPI communication between a STM32F4 MCU and an ADE7868A.
The connection is straight between MISO, MOSI, SCK, /SS, /RESET.
We do what follows:
Set /SS high
Reset the ADE7868 toggling low /RESET for 5ms
Set /SS low then high for 3 times with a 5ms period
Write via SPI 0x0 in the CONFIG2 register at a speed of 650Khz more or less (we tried other speeds, too)
Read back CONFIG2
Read a register got from the datasheet
We get something on the MISO pin that is compatible with a SPI answer but checking with a scope its Vpp (V peak to peak) excursion is very narrow (300mV) and oscillates around 3.3V, never going to GND.
If we pull-down the MISO, it always remains to GND.
We observed the same behaviour on 2 different boards.
The ADE7868A seems to be running as VREF is correct and the crystal oscillates fine. Moreover, the IRQ gets asserted upon reset.
With the oscilloscope we verified the other pins and they behave as expected: data are transmitted correctly to the ADE.
PSM0 is selected, so no power saving is active.
Could you share the schematic for the connection of the SPI pins, it would be useful to take a look.
The MISO pin is the data output pin for the ADE7868A, the pin does not need a pull-up or pull-down, make sure that the MCU isn't trying to drive that pin with a high or low. It almost sounds like externally it is being driven high if the data isn't going low from the 3.3V.