User manual
Programmer’s Guide Page 58 of 64
3.18.6. Frequency Counter (mode 6)
This is an option available for the DC140 and DC135 digitizers. It is implemented with a signal counter that counts
trigger signals from the user-requested channel. A time counter generates the user-programmed aperture time, during
which the measurement is performed.
The user-requested signal channel has to be programmed for the expected signal characteristics; the standard config
functions should be used to set the full-scale, coupling, offset and trigger threshold. The HF trigger mode may be set
by the driver software on the basis of the user-supplied target frequency value. In order to obtain the best results, it is
recommended to adjust the full scale and offset so that they span the expected input signal. In addition, the trigger
threshold should be set to approximately the center of the signal voltage range. Calls to AcqrsD1_configVertical
and AcqrsD1_configTrigClass are needed. If an external time base reference is desired, AcqrsD1_configExtClock
should be called. If the totalize in gate functionality is desired the source of the gate must be set with the function
AcqrsD1_configControlIO, with the parameters connector = 1 (I/O A) or 2 (I/O B) and signal = 9. Note that when
this mode is in use the Enable trigger input (signal = 6) functionality of AcqrsD1_configControlIO cannot be used.
The function AcqrsD1_configFCounter sets the parameters specific to the frequency measurements.
AcqrsD1_configFCounter(instrID, channel, type, targetValue, apertureTime,
0.0, 0);
Comments:
• Channel numbers run from 1 to the available number of signal channels in the digitizer.
• The value type is 0 for Frequency, 1 for Period, 2 for Totalize by Time and 3 for Totalize by Gate.
• The targetValue is an estimator of the expected result. If no estimate is possible, use the value 0.0. This
value is only used to activate the HF trigger mode which extends the useable frequency range. By default,
the frequency range is extended except:
type
Measurement
Divide by 1
0
Frequency
if targetValue is smaller than 1 kHz (1000.0) and larger than 0.0
1
Period
if targetValue is larger than 1ms (0.001)
2
Totalize by Time
always (the HF mode is never used)
3
Totalize by Gate
always (the HF mode is never used)
• The apertureTime defines the minimum time for a frequency measurement (it may be longer if the
frequency is very low!). In the Totalize by Time mode, the value of apertureTime determines the time
window during which the input pulses are counted.
The frequency counter mode is set with the function AcqrsD1_configMode, with mode = 6.
After configuring the instrument parameters, the measurement sequence is started with the function
AcqrsD1_acquire. This function returns before the measurement is terminated. The user must wait until it is
terminated with the functions AcqrsD1_acqDone or AcqrsD1_waitForEndOfAcquisition. For the case of Totalize
by Gate the program must stop the acquisition by making a call to the function AcqrsD1_stopAcquisition.
FC results can be readout with the function AcqrsD1_readFCounter. The result is always a single double precision
number whose units are those appropriate for the type of measurement chosen.
3.18.7. SSR – Sustained Sequential Recording (mode 7)
SSR mode is supported by certain AP235/240 and U1084A models. SSR functionality includes a ping-pong memory
buffer architecture. The processing memory is split in two so that module can continuously acquire data into one
memory bank while the other bank is read into the host processor. This technique is particularly useful for
continuous acquisition of data bursts at a sustained trigger rate.
For further information please refer to section 3.5 of this document.
3.18.8. DDC – Digital Down-Conversion (mode 12)
Digital Down-Conversion is currently supported only on the M9202A model. It allows for operation as the
Intermediate Frequency (IF) digitization element in a digital receiver. For futher information on the configuration
and operation, please refer to the ‘Digital Down-Conversion’ topic in the MD1 User Guide & SFP Help system.