Nrf5340 SPIS CSN rise time specifications

[skajam66]

Hi,

I have a nrf5340 SPIS peripheral being driven by an STM32H753 micro. Data transfer works fine except when I connect a scope probe to the CSN pin. With the scope probe connected, SPIS no longer generates interrupts.  This happens with both a PicoScope 3000 and a Rigol 1074Z both using a X1 probe.

With the scope probe attached, the measured rise time (de-assert) (10%-90%) is approx 24ns, the fall time (assert) is approx. 29ns.

How do I determine if these timings are within specification? The Product Specification document provides typical values for GPIO pins but I see no maximum timings.

Can you advise?

Kind regards,

AC

[Kenneth]

Sounds very odd, scope probes are typically high impedance so they should not impact digital gpios much. I would look into whether you have also connected the ground of the probe to the ground of the board, before connecting the probe. 

Kenneth

[skajam66]

Hi Kenneth,

The scope probe impedance is 1M ohm. The problem only occurs when the scope probe ground is connected to board ground.

Can you point me to any documentation on what the maximum (slowest) rise and fall time requirements are for a GPIO pin?

Regards,

AC

[Kenneth]

skajam66 said:

Can you point me to any documentation on what the maximum (slowest) rise and fall time requirements are for a GPIO pin?

There is no such limit, it will trigger on >0.7*VDD or <0.3*VDD.

Kenneth