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X-NUCLEO-IDB04A1(BlueNRG 4.0) problems with SPI_IRQ signal level

Question asked by serene.orland on Aug 18, 2016
Greetings everyone.

I've recently lay my hands down on this devboard, but, I only have STM32F4Discovery board to pair it with. So, I started with simple checking - I'm pulling RESETN to high level, to tell BlueNRG chip that it's should turn-on. I've connected oscilloscope to the SPI_IRQ output pin (nothing connected), and seeing very strange thing - signal goes from GND to somewhere about -1.5VDC. I'm wondering, since there should be clear positive change, not negative towards GND. Is it could be some problems with powering up this nucleo board ? I've take 3.3V from discovery board. When I'm trying to connect this pin to the STM32F407 on the discovery, there are complete mess - signal spikes, pull-down resistor is configured on the input.

I've come to the point, that I don't understand, what's going on with the SPI_IRQ level at all. Any help will be much appreciated.