Generally speaking, you want to use the hardware based clocking, since the hardware usually has the highest resolution clock.
When we introduced the Time Base concept, it was to address the new feature that allowed more than one DAQ device to be connected to the PC. Each device may have its own clocking, and some allow you to connect and synchronize multiple devices (Master/Slave clocking).
One major driver, the IOtech driver, decided to stay within the original Driver API, which allows only one time base, but they made changes in the driver to handle master/slave and sample rate decisions.
Other drivers embraced the Time Base concept, and were developed using the "Extension DLL API", starting with the National Instruments driver, and picked up by most driver developers, including Measurement Computing, UEI, instruNet, and many others.
So, DASYLab now shows you timing sources from at least two devices --
Driver Timebase is associated with the installed driver - Sound Card, Demo, or IOtech, typically.
DASYLab Timebase is a software timed source, usually used for slower (less than 100 samples/sec) timing
As you add drivers, you will be exposed to that manufacturer's choice of timing:
National Instruments NI-DAQmx - timing is set in NI Measurement & Automation (MAX)
You have choices of 1 sample on demand, n samples, continuous
Each task has its own timing, so one board may have a timebase for Analog Input, Analog Output, Digital Input, Digital Output, etc.
Measurement Computing MCC-DRV
You have two timebases available for most devices, Hardware clocked or software clocked.
Some devices only allow hardware clocking for one subsystem - the other subsystems would then use the software clock
Some devices only allow a single sample rate (USB-TC, USB-TEMP are 2 s/sec)
Some devices use the settings in instaCal to determine allowed sample rates (USB-2416, USB-2408); individual channel choices may limit the overall (aggregate) sample rate.
Analog/Digital output timing can be configured "using the input timing" or with driver based timing - many devices only support software clocked ("slow") timing on outputs.
UEI - time bases are not created until you create modules that require them
InstruNet - time base is determined by a mix of the DASYLab time base and the individual channel settings
If you open a worksheet and you see a time base that is in (parentheses) - the driver or hardware was not found, but the worksheet remembers it.
Many modules are software data generators - the Generator, the Switch, the Slider, and they offer an option to select one of the available time bases. If you use a switch, for example, to control a relay, the switch timing should match the other inputs of the relay. The switch and the slider also offer a "with input" choice, which allows you to wire an input to them, to force the module timing to match the input timing.
Some Input/Output modules have to use software timing on the data - the RS232 Input, for example. It has to assume that the input samples are not equidistantly spaced, and tags the timing with "triggered". You can force it to use hardware timing in the Options, and fill the data block with old data until new data is received.
Confusing? Yep.
What's the right choice?
Hardware vs. software clocking - for sample rates above 100 samples/second, you will want hardware clocking. For slower rates, you may be forced to use software clocking.
DASYLab vs. Driver vs. Timebase A HW vs. Timebase B SW
I would use the device's clock whenever feasible. It's more reliable and accurate than the PC clock.
So, for Measurement Computing USB "pods" (I like that word!) - use the MCC-DRV timebases when ever possible.
Datashuttle... are you in the UK? The original Datashuttle is long gone, and only used the Driver timebase.
The UK sold (sells?) a version of the IOtech PersonalDAQ 54/55/56 products as a Datashuttle.
Funny that you should mention tetris... someone may have written a tetris module for DASYLab as a exercise.
Measurement Computing (MCC) has free technical support. Visit
www.mccdaq.com and click on the "Support" tab for all support options, including DASYLab.
