Chapter 4 Register Descriptions
© National Instruments Corporation 4-5 SCXI-1120 User Manual
Slot 0 Register Descriptions
Slot 0 has three registers. The Slot-Select Register is a 16-bit, write-only register that determines
with which slot the data acquisition board will speak when SLOT0SEL* is released high. In the
case of the SCXI-1001 chassis, the Slot-Select Register also determines in which chassis the
desired slot is. The FIFO Register is a 16-bit, write-only register used for storing the Slot 0 scan
list that determines the chassis scan sequence. The Hardscan Control Register (HSCR) is an
8-bit, write-only register used for setting up the timing circuitry in Slot 0. The Slot-Select
Register is written to by using the SLOT0SEL* line. The HSCR and the FIFO Register are
written to as if they were registers located on modules in Slots 13 and 14. You should maintain
software copies of the Slot-Select Register, HSCRs, and all the Slot 0 scan lists that correspond
to the writes to FIFO Registers.
If you are using multiple chassis, it is important to understand the architectural differences of the
Slot-Select Register as compared to the HSCR and the FIFO Register. Although each chassis
has its own physical Slot-Select Register, all are written to at the same time. The jumper settings
in Slot 0 of a chassis determine with which chassis number Slot 0 is identified. From the
software perspective, only one Slot-Select Register exists in a system composed of multiple
chassis. The HSCR and FIFO Register, on the other hand, are unique to each chassis and you
must program them separately.