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 section in Chapter2,
Configuration and Installation. The rear signal connector pin equivalences
to the different National Instruments data acquisition boards are given in
Table5-1. See also AppendixE, SCXI-1121 Cabling. 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