National Instruments SCXI-1121 - Manual (Page 69)

Chapter 3 Theory of Operation
© National Instruments Corporation 3-7 SCXI-1121 User Manual
Digital Control Circuitry
Figure 3-4 diagrams the SCXI-1121 digital control.
Figure 3-4. SCXI-1121 Digital Control
The digital control section consists of the Configuration Register and the
Module ID Register.
The Configuration Register is a two-byte, serial-in parallel-out shift
register. Data is received on the MOSI line from either Slot 0 or the data
acquisition board when SS* is enabled and D*/A indicates data transfer
(D*/A low). The Configuration Register provides temperature channel
selection and channel selection, and configures the SCXI-1121 for
scanning options. All the control bits are fed into a latch before being
routed to the rest of the module. The channel-select bits are taken directly
from the shift register. Complete descriptions of the register bits are given
in Chapter 4,
Register Descriptions . Writes to the Configuration Register
require the following steps:
1. SS* goes low, enabling communication with the board.
2. D*/A goes low, indicating that the information sent on the MOSI line
is data.
Module ID Register
Configuration
Register
Serial Data Out
Input Channel
Select
Output
Stage
Control
Hardware
Scan
Control
SCANCLK
Path
Control
Buffered
Serial Data In
Buffered Digital
Control Signals