National Instruments SCXI-1120 - page 46

Configuration and Installation Chapter 2
SCXI-1120 User Manual 2-30 © National Instruments Corporation
T
low
T
high
SERCLK
SERDATIN
SERDATOUT
T
setup
T
hold
T
delay
Tlow Minimum low time 65 nsec minimum
Thigh Minimum high time 400 nsec minimum
Tsetup SERDATIN setup time 200 nsec minimum
Thold SERDATIN hold time 200 nsec minimum
Tdelay SERDATOUT delay 350 nsec maximum
Figure 2-14. Serial Data Timing Diagram
After the Slot-Select line to an SCXI-1120 has been asserted, you can write to its Configuration
Register and read from its Module ID Register using the following protocols. The contents of
the Module ID Register are reinitialized by deasserting Slot-Select. After the 32 bits of data are
read from the Module ID Register, further data will be zeros until reinitialization occurs.
To write to the Configuration Register, follow these steps:
1. Initial conditions:
SS* asserted low.
SERDATIN = don't care.
DAQD*/A = 0 (indicates data will be written to Configuration Register).
SLOT0SEL* = 1.
SERCLK = 1 (and has not transitioned since SS* went low).
2. For each bit to be written:
Establish the desired SERDATIN level corresponding to this bit.
SERCLK = 0.
SERCLK = 1. Clock the data.
3. Pull SLOT0SEL* low to deassert the SS* line and establish conditions for writing a new
slot-select number to the Slot 0 Slot-Select Register.
4. If you are not selecting another slot, you should write zero to the Slot 0 Slot-Select Register.
Figure 2-15 illustrates a write to the SCXI-1120 Configuration Register of the binary pattern:
10000011 00001111