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If I keep pressing the Turbo Button. Which sequence is right ?
一. 11110000111100001...
二. 10000000100000001...

1 = Pressed
0 = Released

My emulator is the sequence 一. Instead of according the CPU cycles to toggle the Button state, I use
the video frames count to do it(really weird).

Counting video frames is a perfectly fine way to do turbo, seeing as the games themselves count video frames to see when to read the controller.

Now to your question: Yes, you'll want it to do option one, a 50% duty cycle (about as many 1's as 0's). You'll probably want to let the user choose one of several different fire rates: 11110000 (7.5 Hz), 111000 (10 Hz), 1100 (15 Hz), and 110 (20 Hz).

Given turbo buttons weren't really part of the original hardware there's no wrong or right way to do it. I think real controllers with turbo buttons did the 50% square wave thing though, if you wonder.

There're some games which the character will JUMP if you press the Button A + Button B.
When I press the Turbo Button A + Turbo Button B of FCEUX, the character does JUMP. But when I do the same action on my emulator, the character does NOT JUMP.

Why?

If you want turbo to cause a game to perform actions that it performs only when both buttons are pressed, you need to make turbo for both buttons operate in phase.

If A and B are out of phase, as below, no jump will be read.

Frame 1 AB: 01
Frame 2 AB: 01
Frame 3 AB: 10
Frame 4 AB: 10
Frame 5 AB: 01
Frame 6 AB: 01
Frame 7 AB: 10
Frame 8 AB: 10

If A and B are in phase, as below, a jump will be read.

Frame 1 AB: 11
Frame 2 AB: 11
Frame 3 AB: 00
Frame 4 AB: 00
Frame 5 AB: 11
Frame 6 AB: 11
Frame 7 AB: 00
Frame 8 AB: 00

Sik wrote:Given turbo buttons weren't really part of the original hardware there's no wrong or right way to do it. I think real controllers with turbo buttons did the 50% square wave thing though, if you wonder.

Well, there were official Nintendo-licensed turbo controllers, the MAX and Advantage.

Let's not forget Master Takahashi's ability to press a button at 16Hz.