Chapter 4 Register Descriptions
© National Instruments Corporation 4-9 SCXI-1121 User Manual
FIFO Register
The FIFO Register is used to add entries to the Slot 0 FIFO. The FIFO contains the Slot 0 scan
list. Each entry contains a slot number to be accessed, and a count number to determine the
number of samples to be taken from that slot. To write to the FIFO Register, follow the
procedure given in the Register Writes section of Chapter5, Programming, using 14 as the
slot number, and writing 16 bits to the FIFO Register. The register will shift in the data present
on the MOSI line, bit 15 first, when Slot 14 is selected by the Slot-Select Register. The Slot0
scan list is created by consecutive writes to the FIFO Register. Each write creates a new entry
at the end of the scan list. The maximum number of entries is 256. To clear the FIFO of all
entries, clear the HSRS* bit in the HSCR.
Type: Write-only
Word Size: 16-bit
Bit Map:
Bit Name Description
15-11 X Don’t care bits—Unused.
10-7 MOD<3..0>Module Number—The value of these bits plus
on determines the number of the slot to be accessed for this
scan entry. For example, to access Slot 6, MOD<3..0>
would be 0101.
6-0 CNT<6..0> Count—The value of these bits plus one determines how
many samples will be taken before the next scan list entry
becomes active. A value of zero corresponds to one sample
and a value of 127 corresponds to 128 samples.
15 14 13 12 11 10 9 8
X X X X X MOD3 MOD2 MOD1
76543210
MOD0 CNT6 CNT5 CNT4 CNT3 CNT2 CNT1 CNT0