scxi channel strings

[David Lewis]

I'm trying to configure an SCXI-1000 chassis that contains an SCXI-1200 in
slot 1, an SCXI-1121 with a 1320 terminal block in slot 2, and an SCXI-1121
with a 1321 terminal block in slot 4.

The SCXI-1200 is the only DAQ board present, and it is connected via a
parallel port cable to a PC. I've got to the point where the MAX indicates
that "the chassis is verified", and I can run a test panel with the
SCXI-1200. I've connected a known voltage to channel 0 of the SCXI-1121 in
slot 2 via a 1320 bolted on the front. I can't get the test panel to
measure it.

I have seemingly conflicting information from NI knowledgebase about the
scxi channel string I would need to use.

For instance, from the knowledgebase paper
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/6fc83b7ac9aca5788625615b00823d65?OpenDocument
"The format of the channel string is as follows:

obx ! scy ! mdz ! channels
obx is the onboard DAQ device channel, with x representing a particular
channel where the multiplexed channels are sent. This value is 0 for DAQ
channel 0 in a single-chassis system"

And then, from the knowledgebase paper
http://digital.ni.com/public.nsf/3efedde4322fef19862567740067f3cc/261b5b9dc65a3a4a8625695a006c97cd?OpenDocument
"The general format of the SCXI channel string is OBz!SCx!MDy!a, where z is
the device number of the DAQ board connected to the chassis, x is the SCXI
chassis number, y is the module number, and a is the channel number"

I can't seem to sort this out. The problem seems to be that the SCXI-1200
is a DAQ board, but it is also an SCXI module, and as such an oddball, it is
some kind of exception when it comes to the channel strings.

Also, there is conflicting information in the knowledgebase about the way to
set up the SCXI-1200 with one paper definitely stating that you can only use
the 1200 in RSE mode and another stating that you can only use it in NRSE
mode when it is used with modules such as the 1121 in a chassis.

Can anyone suggest a solution? Thank you.

[Dr._Imad]

Hello David,

I looked at an application that I wrote few years ago using an scxi system (during the days of win 3.1 and win 95).
The general syntax is

sc1 ! md3 ! 0:5

here I have scxi id 1, module 3, Channels 0 thru 5


The scxi 1200 was in slot 1, connected to the printer.
it works like a daq card in the sense the channel syntax are like that of a daq card (no scxi channel syntax). Note also the reverse order of the channels order (exactly like PCI 1200 daq card)., meaning index 0 of the voltage array (in the example corresponds to channel 7 data, etc)

One thing, we discovered that runing an SCXI chassis with a an SCXI-1200 was not a good at all (instead of using a daq card), once in a while the computer gave a blue screen(again, during
the days of win 3.1 and win 95)

My understanding now is that the newest versions of Nidaq may not be supporting 1200 devices anymore (may want to verify that)

The attached vi has example channels copied from the diffwerent vi's in the application

[Sean_C.]

Hello David,

Thank you for contacting National Instruments.

You are correct in the syntax of the SCXI channel strings. The "x" in obx! represents the device number of the DAQ board that connects to the SCXI Chassis. All the input signals from the SCXI chassis are multiplexed and fed into channel 0 of the DAQ board.

You are also correct that the SCXI-1200 behaves differently than other SCXI modules. Because it is a DAQ card, it is assigned a device number. To access the 1200's channels you only use the device number and channel numbers, not the SCXI channel strings.

I hope this helps,

Sean C.
Applications Engineer
National Instruments