National Instruments SCXI-1161 - Manual (Page 22)

Chapter 2 Configuration and Installation
SCXI-1161 User Manual 2-6 © National Instruments Corporation
Jumper W2
Position 1 connects the SCXIbus MISO line, after buffering, to
the SERDATOUT pin of the rear signal connector. This is the
factory-default setting. In this setting, along with the proper setting of
jumper W1, the data acquisition board can read the Module ID Register
of the SCXI-1161. See the SCXI Register-Level Programmers Manual,
for information on reading the Module ID Register. See the cable
installation guide of your cable, for the pin equivalences of the
SCXI-1161 rear signal connector and the data acquisition board I/O
connector.
Position 3 disconnects SERDATOUT from the SCXIbus MISO line.
Using Jumpers W1 and W2
If you do not connect a module to a data acquisition board, the positions
of jumpers W1 and W2 are irrelevant. Jumpers W1 and W2 give the data
acquisition board access to the MISO line on the backplane. You can
use the MISO line to read the Module ID Register of modules. National
Instruments software does not use this ability. You must indicate to the
software which module is in which slot.
An open-collector driver drives the SERDATOUT line. An
open-collector driver actively drives low or goes to a high-impedance
state, relying on a pullup resistor to make the signal line go high. When
using a single chassis, set both jumpers W1 and W2 to position 1 on
the SCXI-1161 that is connected to the data acquisition board. In this
setting, the module drives MISO to SERDATOUT and connects the
necessary pullup resistor to the SERDATOUT line. When using
multiple chassis, set jumper W2 to position 1 on all of the SCXI-1161s
that are cabled to the data acquisition board. Set jumper W1 to
position 1 on only one of the SCXI-1161s that are cabled to the data
acquisition board. It does not matter which of the SCXI-1161s that are
cabled to the data acquisition board has the pullup connected. Set
jumper W1 to position 3 on all of the other SCXI-1161 modules that are
cabled to the data acquisition board. If too many pullup resistors are
attached to the SERDATOUT line, the drivers cannot drive the line low.
Tables 2-1 and 2-2 list the description and configuration of the jumper
settings.