[Solved]What is the difference between zapper trigger and Up

[geod]

From my understanding both set the bit 4 of the console port so it should be the same.
I'm testing with zapper_stream rom of rainwarrior from https://forums.nesdev.com/viewtopic.php?f=9&t=13021 with Mesen, Bizhawk, FCEUX.
If i select a zapper for the port 2, the rom works as expected and detect the trigger pulling but if i select a second gamepad and press Up button nothing happens. So it must have something wrong in my understanding.
Can someone help me pointing out the issue pls?
Thanks!

[lidnariq]

The standard controller does not give you all the bits simultaneously. When you read $4016 or $4017, you only get one button at a time, and that from the least significant bit.

The zapper, in contrast, only has 2 "buttons", and those are received simultaneously. (Unless you're on the Vs. System)

[geod]

I get it now, thank you