What is the purpose of a period in ibcmd calls?

[ceetee]

I'm converting an old GPIB calibration script and am seeing periods in the oddest of places and cannot determine the reason. Can someone explain?

For ibcmd I can understand this...

ibcmd(GPIB0, "?U!", 3 (0x3))
ibwrt(GPIB0, "MEASU:MEAS1:V...", 17 (0x11))
ibcmd(GPIB0, "_?", 2 (0x2))

But what about this one?

ibcmd(GPIB0, "?_5.", 4 (0x4))
ibcmd(GPIB0, "A", 1 (0x1))
ibrd(GPIB0, "P", 1 (0x1))
ibcmd(GPIB0, "._?", 3 (0x3))

It appears to be only seen when working with the board.. the Multiline interface message ends with a period then the untalk unlisten calls begin with one.

What is the reason behind this additional period? I would think that it would overwrite MLA/MTA's in the same command.

[NI-488.2 master]

For the first ibcmd("?_5."): The result will be that devices at GPIB addresses 21 and 14 will be addressed to listen. Keep in mind that on GPIB there can be multiple listeners, but only a single talker.

For the second ibcmd("A"): The result will be that the device at GPIB address 1 will be addressed to talk.

The last ibcmd("._?") does not make much sense. The UNT(_) and UNL(?) will override the previous MLA14(.).

Hope this sheds some light on your problem.

Craig A.
National Instruments Engineer

[ceetee]

Ding! The lightbulb just went off. Thanks Craig.. now what I'm looking at makes perfect sense.

[ceetee]

Two additional questions.

>>For the second ibcmd("A"): The result will be that the device at GPIB address 1 will be addressed to talk<<

Where do you get 1 from the A?

Is the P in the ibrd an indication of the set bit masks?

[NI-488.2 master]

>> Where do you get 1 from the A?

An ASCII A, or HEX 41 corresponds to MTA1. Look in NI-488.2 Help for "IEEE 488 command messages" for a full table of command message definitions.

>> Is the P in the ibrd an indication of the set bit masks?

Is this the result of looking at an NI-Spy capture, or is this how the actual code was written? If this was from the Spy capture, the "P" was the data read from a device.

Craig A.
National Instruments Engineer