Channel Trigger | Trigger modes and appendant registers |
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Triggerlevel | ±50 mV | ±100 mV | ±200 mV | ±500 mV | ±1 V | ±2 V | ±5 V | ±10 V |
127 | +49.6 mV | +99.2 mV | +198.4 mV | +496.1 mV | +992.2 mV | +1.98 V | +4.96 V | +9.92 V |
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126 | +49.2 mV | +98.4 mV | +196.9 mV | +492.2 mV | +984.4 mV | +1.97 V | +4.92 V | +9.84 V |
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64 | +25.0 mV | +50.0 mV | +100.0 mV | +250.0 mV | +500.0 mV | +1.00 V | +2.50 V | +5.00 V |
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2 | +0.78 mV | +1.56 mV | +3.1 mV | +7.8 mV | +15.6 mV | +31.3 mV | +78.1 mV | +156.3 mV |
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1 | +0.39 mV | +0.78 mV | +1.5 mV | +3.9 mV | +7.8 mV | +15.6 mV | +39.1 mV | +78.1 mV |
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0 | 0 V | 0 V | 0 V | 0 V | 0 V | 0 V | 0 V | 0 V |
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Stepsize | 0.39 mV | 0.75 mV | 1.5 mV | 3.9 mV | 7.8 mV | 15.6 mV | 39.1 mV | 78.1 mV |
The following example shows, how to set up a one channel board to trigger on channel0’s rising edge. It is asumed, that the input range of channel0 is set to the the ±200 mV range. The dezimal value for SPC_HIGHLEVEL0 corresponds then with 62.5 mV, wich is the resulting triggerlevel.
SpcSetParam (hDrv, SPC_TRIGGERMODE , | TM_CHANNEL); // Enable channel | trigger | mode | |||||
SpcSetParam | (hDrv, | SPC_TRIGGERMODE0, | TM_CHXPOS ); | // | Enable channel | trigger | mode | |
SpcSetParam | (hDrv, | SPC_HIGHLEVEL0 , | 40 | ); | // | Sets triggerlevel to 62.5 mV |
Reading out the number of possible trigger levels
The Spectrum driver also contains a register, that holds the value of the maximum possible different trigger levels considering the above men- tioned exclusion of the most negative possible value. This is useful, as new drivers can also be used with older hardware versions, because you can check the trigger resolution during runtime. The register is shown in the following table:
Register | Value | Direction | Description |
SPC_READTRGLVLCOUNT | 2500 | r | Contains the number of different possible trigger levels. |
In case of a board that uses 8 bits for trigger detection the returned value would be 255, as either the zero and 127 positive and negative values are possible.
The resulting trigger step width in mV can easily be calculated from the returned value. It is assumed that you know the actually selected input range.
To give you an example on how to use this formular we assume, that the ±1.0 V input range is selected and the board uses 8 bits for trigger detection.
Input Rangemax – Input Rangemin Trigger step width =
Number of trigger levels + 1
+1000 mV –
255 + 1
The result would be 7.81 mV, which is the step width for your type of board withing the actually chosen input range.
68 | MC.31xx Manual |