TTL Pulse width recognition

[paekdu419]

Hi
I am new to the system and have two questions for you.
1. what would be a minimum and maximum TTL pulse width recognition for Biosemi software?
2. If I analyze bdf file, then which end (up or down or somewhere between) can be recognized as a marker?

Thanks in advance!

[Coen]

The trigger length should be at least the duration of a (hardware) sample (e.g: > 0.5 millisecond on speedmode 4, > 61 microsecond on speedmode 7). Decimation to a lower sample rate in software works by applying an OR function on successive groups of trigger samples (e.g. if any of the samples in a group shows a high trigger, then the resulting trigger is High). Therefore, you should always use positive trigger logic (Low level is no trigger, High level is trigger). Negative trigger logic results in missed triggers if the trigger length is less than the duration of the eventual decimated sample.

The markers are stored in the last channel of the BDF file, see http://www.biosemi.com/faq/trigger_signals.htm. The coding is digital, you should decoded the trigger/status channel bit by bit (not as an 24bit representation of an analog value)

Best regards, Coen (BioSemi)

[marialaura]

Hi,
I read from different posts that the function keys F1-F8 are by standard coupled to trigger lines 9-16. A key press makes the respective trigger line high. Sounds good. I made and it works.
What I'm still wondering is what does it mean that "the tringger length must be at least the duration of a sample". In my test I press F1 and make the trigger line high, but it is high only for the time of the pressure!If I want to maintain it high (for an amount of millisecond or second)I need to press the key continuously. Is it right? Does it means that through function key I can only set a "discrete" trigger?

Thanks in advance.

best reegards, marialaura

[Coen]

The trigger lengths values refers to the trigger signals coupled to the trigger port on the USB receiver.

When triggers are controlled with the function keys, the line remains high approximately as long as the key is pressed.

Best regards, Coen (BioSemi)