User guide

Charnwood Dynamics Ltd. Coda cx1 User Guide – Reference IV-6
CX1 USER GUIDE - COMPLETE.doc 26/04/04 161/162
Digital Trigger Outputs
Two trigger outputs may be defined by the user, using any of the digital channels (1 – 4), via
the Digital Trigger Setup dialogue: CODA: Define Trigger 1..., Define Trigger 2...
The trigger channels react to changes in marker positions. Each channel can be configured
to ‘trigger’ (go low) when a selected marker passes a defined threshold position in X, Y, or Z
(or any combination) in either the positive or negative direction. The position is relative to the
current origin.
Digital output triggering is enabled in the Acquisition Setup dialogue (CODA: Acquisition
Setup...), and is active during data acquisition or when the real-time stick figure display is
open (and is being updated) (CODA: Display Stick Figure). Triggering is not active during
acquisition standby (although the special digital channels 5 - 8 are active during acquisition
standby - see below), and is not active when (only) the real-time marker text display is open
(CODA: Display Marker Positions).
During data acquisition, the trigger output channels change state within three epoch periods
of the trigger marker passing the threshold position (i.e. within 15ms when acquiring at
200Hz). There can be occasional longer delays due to PC operating system interrupts.
During real-time stick figure marker display, the trigger output channels normally change
state between 15 and 70ms after the trigger marker passes its threshold (the real-time
display is updated every 55ms). There may be longer delays if the PC operating system
switches tasks.
Special Input-Outputs
Digital channels 5 - 8 have pre-programmed I/O functionality, and so cannot normally be
used as general-purpose inputs.
Channel 5: Output: Low during Auto-start Acquisition Standby (Standing by for
Markers...)
(Can be used to reset a force platform interface, for example.)
Channel 6: Output: Low during data Acquisition.
Input: Pulled low during Auto-start Standby to start acquisition (regardless
of markers).
Channel 7: Output: When acquisition triggering is enabled, changes state at the
beginning of each epoch (synchronized to the cx1 strobe). Thus appears
as a square-wave of period = 2 x epoch period.
Channel 8: Output: Late-trigger flag: when acquisition triggering is enabled, goes low if
a marker position trigger output occurs later than 3 epochs after the marker
moved past the threshold position.
If acquisition triggering is not enabled, channels 7 and 8 may be used as general-purpose
inputs.
During data acquisition, all 15 digital channels are always recorded.