National Instruments SCXI-1121 Manuel D’Utilisation

3.

The serial data is available on MOSI and SPICLK clocks it into the 
register.

4.

SS* goes high and D*/A goes high, indicating an end of 
communication. This action latches the Configuration Register bits.

When the SCXIbus is reset, all bits in the Configuration Register are 
cleared.

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-1121 module ID is hex 00000002.

The SCXIbus provides analog power (±18.5 VDC) that is regulated on the 
SCXI-1121 to ±15 VDC, a guard, an analog bus (AB0±), and a chassis 
ground (CHSGND). AB0± buses the SCXI-1121 output to other modules 
or receives outputs from other modules via the SCXIbus. Refer to the 

 section later in this chapter for more information. The guard 

guards the analog bus, and can be connected via jumper W33 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-1121 output and the data acquisition board. This is fully 
described in the following section.

Figure 3-5 is a diagram of the analog input block.