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They are documented in the Programmer's Reference Manual. A program can always be started with the digitizer in an uncalibrated state and data taken can be used for many kinds of testing. However, as soon as good data respecting the specifications of the instrument is required a calibration of at least the current acquisition state is needed. The full internal calibration has the advantage that it generates the calibration constants needed for any possible configuration of the instrument; its disadvantage is the time taken. If a more selective calibration is done it will allow the generation of good data in the current acquisition state. This calibration will remain useable whenever that acquisition state is used again for as long as the temperature of the instrument does not change significantly. A fast calibration of a channel in a configuration can be done in around a second. Many applications can save time by only performing calibration for the configurations that will actually be used. An application program will close devices if it exits normally. When a 10-bit digitizer is closed in this way its power consumption will be reduced. This has the consequence that if another application program is started later an appropriate warm-up period may have to be respected before a calibration is called for and full performance expected. 3.7. ASBus2 The digitizers may be used in applications that require many data acquisition channels. In such cases it is possible to use more than one digitizer in a standard CompactPCI/PXI crate. Each DC Series 10-bit digitizer includes ASBus2, a proprietary high bandwidth auto-synchronous bus system that allows multiple digitizers to work together synchronously. ASBus2 distributes both the clock and trigger signals along a plug-in front panel bus, between all the digitizers that participate in the system. It allows any digitizer to act as the trigger source and any other digitizer to act as the clock source (acquisition master), enabling all the digitizers to be clocked at the same time. Synchronizing the clock signals between the devices improves the accuracy of cross-channel measurements and is essential for accurate time correlation between signals on different channels. ASBus2 is intended to connect modules of the same type, i.e. of the same model number, although some exceptions to this rule might be possible. If modules with the same model number, but different memory length options, are connected only the shortest memory length can be used. The ASBus2 connector is located on the front panel of each module. Bridges are used to connect adjacent modules for synchronization. An ASBus2 multi-instrument is activated through software by a function call. Up to 5 6U modules, or 3 3U modules, may be synchronized with the ASBus2. More detailed information and the commands required to set up the ASBus2 clock and trigger distribution are included in the Programmer's Guide and Reference manuals. 3.8. Special Front Panel Inputs and Controls Connector Function MMCX CLK IN 50 . External Reference or External Clock Input MMCX I/O A User configurable (see below) MMCX TR OUT Signal occurs after an accepted TRIGGER. MMCX I/O B User configurable (see below) The I/O A and I/O B signals are 3.3 V compatible CMOS. This means that, on input, low is < 0.7 V and high must be in the range [1.7 V, 5.0 V]. An unconnected signal will be high. This definition ensures TTL compatibility. On output, the low level will be in the range [0 V, 0.7 V] and the high level in the range [1.7 V, 3.3 V] for HiZ. The high level output will typically give 0.8 V into 50 .. The I/O A or B connectors can be used for an Enable trigger input or the following output signals: 10 MHz reference clock, Acquisition skipping to next segment, Acquisition is active, Trigger is armed. 3.9. External Trigger Output When the digitizer is ready to be triggered and a valid trigger signal occurs, a trigger output is generated for external use. It is always available on the Front Panel Trigger Out MMCX connector. The pulse ends when the data acquisition for the trigger in question is complete. GNDGND NOTE: The External Trigger Output functionality is implemented in the hardware. No Trigger Out signal occurs for software-generated triggers such as those of the AUTO mode of AcqirisLive or through the use of the function AcqrsD1_forceTrigger. However, AcqrsD1_forceTriggerEx does generate the signal. Trigger Output Block diagram: The output swing is 1.6 V (± 0.8 V) when unloaded and 0.8 V when terminated on 50 .. The rise and fall times are 2.5 ns typical. The offset can be adjusted, by software control in the range [–2.3 V, +2.3 V] unloaded, or [-1.15 V, +1.15 V] into 50 .. The maximum output current capability is ± 15 mA. As the output is retro-terminated, it is possible to drive a 50 . line unterminated (HiZ) without loss of performance. For a TTL compatible signal, set the offset to 1.0 V and the swing at destination will be +0.2 to +1.8 V. ...

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