GPIB Communications with N3300A DC Load Bank

[Tim_C.]

Hello

I used an example of comminicating with a GPIB device via a CRIO and a NI GPIB-RS232 Converter box.  I am attemting to controll an Agilent N3300A DC Load Bank.

I have a couple questions as my comminications appear to be quite buggy at the time,  for example the instrument may not always reply when I send it an identity query

*IDN? with a labview carrige return concatenated to the end.  This concatenation was in the original example in the write vi.

http://zone.ni.com/devzone/cda/epd/p/id/5978

Other threads speak of not using a carrig return or a line feed but instead using an EOI or EOS termination character.

http://forums.ni.com/ni/board/message?board.id=140&thread.id=12916&view=by_date_ascending&page=1

but I still do not understand what this EOI termoination character is.

****Taken from linked thread

The best default termination character is none. GPIB (IEEE 488.1) defines a special hardware line, EOI, which is asserted with the last byte to signify the end of a transfer. You should rely on this method to terminate a GPIB transfer, as opposed to a termination byte that is stuffed into the bytestream. Some older devices (primarily those that were initially RS-232) use only a EOS character, and that can be CR, LF, or CR-LF, which is why the option exists to terminate a read transfer on EOS with NI-488.2.

Most devices (such as those following the IEEE 488.2 protocol) use both (they send a LF at the end with EOI asserted). Even in that case, however, you should only really be concerned with the EOI since that is the native termination of the GPIB.

*******

I guess I am confused to find an example about communicating RS232 to GPIB in which the write vi uses a carrige return  and in contrast the guidance may be to not use any termination character or

use the EOI or EOS termination character.  WHICH I would really like to know what those chacters are.

Perhaps an important note about all this is that I am trying to control an instrument.  I am not trying to perform any data transfers binary or otherwise.

Thanks

Tim C.

[GovBob]

EOI is not a character, it is a hardware line. See this.

Hope this helps.