Chapter 4 Register Descriptions
© National Instruments Corporation 4-5 SCXI-1121 User Manual
0 FOUTEN* Forced Output Enable—This bit determines whether the
module will drive the MCH0± pins on the rear signal
connector with either the selected channel output or the
MTEMP signal, depending on the state of RTEMP. If
FOUTEN* is cleared to zero, the MCH0± pins will be
driven through a buffer by the selected channel output or
the MTEMP line. If FOUTEN* is set to one, the MCH0±
pins will not be driven by the selected channel output or
MTEMP, unless SCANCON is active (low) and the
SCANCONEN bit is cleared. If the selected channel
output or MTEMP is driving the output buffer, it will drive
Analog Bus 0 if AB0EN is set. If nothing is driving the
output buffer, the SCXI-1121 output will saturate.
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.
It is recommended that you 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.