Chapter 5 Programming
SCXI-1121 User Manual 5-2 www.natinst.com
Register Writes
This section describes how to write to the Configuration Register, HSCR,
and FIFO Register including the procedure for writing to the Slot-Select
Register to select the appropriate slot. For timing specifics, refer to the
Timing Requirements and Communication Protocol
Configuration and Installation
. The rear signal connector pin equivalences
to the different National Instruments data acquisition boards are given in
Table 5-1. See also Appendix E,
. The Configuration
Register, the FIFO Register, and the HSCR are write-only registers.
The different bits in these registers often control independent pieces of
circuitry. There are times when you may want to set or clear a specific bit
or bits without affecting the remaining bits. However, a write to one of these
registers will affect all bits simultaneously. You cannot read the registers to
determine which bits have been set or cleared in the past therefore, you
should maintain a software copy of these registers. You can then read the
software copy to determine the status of the register. To change the state of
a single bit without disturbing the remaining bits, set or clear the bit in the
software copy and write the software copy to the register.
Register Selection and Write Procedure
1. Select the slot of the module to be written to (or Slot 13 or 14). Initial
conditions:
SERDATIN = X
DAQD*/A = X
SLOT0SEL* = 1
SERCLK = 1
2. Clear SLOT0SEL* to 0. This will deassert all SS* lines to all modules
in all chassis.
Table 5-1.
SCXI-1121 Rear Signal Connector Pin Equivalences
SCXIbus
Line
SCXI-1121
Rear Signal
Connector
MIO-16
Lab Board
PC-LPM-16
MOSI
SERDATIN
ADIO0
PB4
DOUT4
D*/A
DAQD*/A
ADIO1
PB5
DOUT5
INTR*
SLOT0SEL*
ADIO2
PB6
DOUT6
SPICLK
SERCLK
EXTSTROBE*
PB7
DOUT7
MISO
SERDATOUT
BDIO0
PC1
DIN6
