GPIB hSR770

[mclaugb]

I'm using a stanford Research SR770 instrument.  I'm trying to read the Y-scale data of Trace 0 out of the instrument in one shot using the command "SPEC?0"  The data coming back is poorly defined in the manual on page .  It is an ASCI array with 400 bins.  The problem comes when I assign the number of bytes to the GPIB read.  If I over-guess the number of bytes, the next several GPIB reads have erroneous data and I have to power down the instrument and take out the GPIB command.  If I under-guess the number of bytes, I get the correct data...but not enough.  Right now, the ideal value appears to be between 5800 and 5900 to get all 400 values.

Any help or thoughts greatly appreciated.

Thanks,
Bryan

[Dennis_Knutson]

With an instrument that is compliant with IEEE-488, you don't have to guess. You can specify some high byte count and the instrument is supposed to assert EOI at which point the read will automatically terminate. You should check with SRS to see if in fact the instrument does assert EOI or if it uses a different termination and is not compliant.