Analog and timing circuitry, Analog input channels – National Instruments SCXI-1120 User Manual
Page 55
Theory of Operation
Chapter 3
SCXI-1120 User Manual
3-8
© National Instruments Corporation
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. The contents of the
Module ID Register are written onto MISO during the first four bytes of transfer after SS* has
been asserted low. Zeros are written to MISO thereafter until SS* is released and reasserted.
The SCXI-1120 module ID is hex 00000004.
Analog and Timing Circuitry
The SCXIbus provides analog power (
±
18.5 VDC) that is regulated on the SCXI-1120 to
±
15 VDC, a guard, an analog bus (AB0
±
), and a chassis ground (CHSGND). AB0
±
buses the
SCXI-1120 output to other modules or receives outputs from other modules via the SCXIbus.
The guard guards the analog bus and can be connected via jumper W46 to the analog ground
reference or can be left floating (a connection can be made by another board).
The data acquisition board analog input and timing is the interface between the SCXI-1120
output and the data acquisition board. This is described in the following section.
Analog Input Channels
Figure 3-5 is a diagram of the analog input block.