ADLINK PCM-9112+ - Manual (Page 44)

36 • Operation Theory
If the signal source are both floating, you should use the differential mode,
and the floating signal source should be connected as the Figure 4.2.4.
AIHn
AILn
n = 0, ..., 7
Floating
Signal
Source
To A/D
Converter
High
Low
GND
Figure 4.2.4 Floating source and differential input
4.2.1 A/D Conversion Procedure
The A/D conversion starts when a trigger is set by the trigger source. The
PCI-9112 provides three trigger modes. See section 4.2.2.
While A/D conversion is in progress, the DRDY bit in the A/D status register
is cleared and indicates that the data is not ready. After the conversion is
completed, the DRDY bit will return to active high (1) level. The converted
data can now be read from the A/D data registers. Please refer to section 3.5
for more information about the A/D status register.
The A/D data should now be transferred into the PC's memory for further
processing. The PCI-9112 provides three data transfer modes that allow
users to optimize the DAS system. Refer to section 4.2.3 for data transfer
modes.
4.2.2 A/D Trigger Modes
In the PCI-9112, A/D conversion can be triggered by an Internal or External
trigger source. The EITS bit of the A/D control register is used to select the
internal or external trigger. Please refer to section 3.4 for details. Whenever
an external source is set, the internal sources are disabled.
If an internal trigger is selected, either the software trigger or time pacer
trigger can be used. The A/D operation mode is controlled by the A/D mode
bits (EITS, TSTS) of the A/D control register (BASE+18). Totally there are
three trigger sources available to the PCI-9112. The different trigger
conditions are specified below: