PCVisionplus
Hardware Reference
Registers
3–39
Rev 02; February 8, 2002
3.4.6.1 Trigger Enable (TRIGEN) R/W
This bit enables external trigger mode. The TRIGSEL bits select the software trigger or external input trigger pulse.
The trigger remains enabled and ready for the next trigger input until disabled by writing a zero to this bit. The trigger
input is ignored if a trigger cycle is currently in progress and TRIGMD disables the latch. If TRIGMD enables the
latch, trigger signals occurring during a triggered acquire cycle are latched, and executed when the current cycle
ends.
TRIGEN
Function
0
Trigger disabled
1
Trigger cycle enabled
3.4.6.2 Trigger Source Select (TRIGSEL) R/W
The three TRIGSEL bits define which of seven trigger signals begins a trigger cycle. PCVisionplus has one software
trigger, three TTL-level Schmidt Trigger inputs, two Opto-coupled trigger inputs, and one RS-422 differential trig-
ger input. The status of all external trigger inputs is available in the PWGV register.
TRIGSEL
Selected trigger input
0
Software trigger
1
15-pin TTL trigger input 0
2
26-pin TTL trigger input 1
3
26-pin TTL trigger input 0
4
Opto-coupled trigger input 0
5
Opto-coupled trigger input 1
6
Differential trigger input 0
7
Differential trigger input 1
3.4.6.3 Trigger Polarity Select (TRIGPOL) R/W
This bit defines the polarity of the external trigger pulse input selected by the TRIGSEL bits. The trigger cycle begins
on a positive going edge.
TRIGPOL
Function
0
External trigger pulse is active low (invert internally)
1
External trigger pulse is active high (no change)
Figure 3–9 illustrates the effect of this bit. Internally, the trigger is fired by the positive edge. In an active high signal,
this is the leading edge. In an active low signal, the positive edge is the trailing edge. Programming TRIGPOL to zero
causes the active low input to be inverted internally, so that the positive edge is the leading edge.
active high input
active low input
active high internally
active high internally
External
Internal
TRGPOL = 1
TRGPOL = 0
Figure 3–9. Trigger Polarity
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