Chapter 3
Theory of Operation
© National Instruments Corporation
3-9
SCXI-1100 User Manual
When you reset the SCXIbus, all bits in the Configuration Register clear.
The Module ID Register connects to MISO on the SCXIbus. The Module ID Register is an 8-bit
parallel/serial-in serial-out shift register and an SPI communication adapter. During the first four
bytes of transfer after SS* is asserted low, the contents of the Module ID Register are written
onto MISO. Zeros are written to MISO thereafter until SS* is released and reasserted. The
SCXI-1100 module ID is hex 00000006.
Analog and Timing Circuitry
The SCXIbus produces analog power (
±
18.5 VDC) that is regulated on the SCXI-1100 to
±
15 VDC, a guard, analog buses (AB0
±
, AB2
±
) and a chassis ground (CHSGND). AB0
±
buses
the SCXI-1100 output to other modules or receives outputs from other modules via the SCXIbus.
The module can use AB2
±
to receive a precision voltage for auto calibration of the PGIA. Refer
to the Calibration section later in this chapter for more information. The guard guards both
analog buses. You can connect the guard via jumper W10 to the PGIA ground reference, or
leave the guard floating (another board can make a connection).
The data acquisition board analog input and timing is the interface between the SCXI-1100
output and the data acquisition board. This interface is described in the following section.
Analog Input and Timing Circuits
Figure 3-6 diagrams the SCXI-1100 analog input and timing circuitry.
