The upper limit of incoming signal frequency when using NRF_TIMER1 as counter

[diode]

I am using NRF_TIMER1 with 16-bit mode and prescaler of 0 as a counter, to count the pulses of an incoming square wave signal in a given time window. What is the upper limit of the incoming frequency for NRF_TIMER1 acting stably?

[diode]

@Aryan: I meant the frequency of the incoming square wave signal to be counted by the NRF_TIMER1. I have updated the description of the question accordingly.