I'm using the Ag532xx_1.05.dll to abstract the VISA communications to a 53230A frequency counter. I do the initial setup, then send a query command and get back "-420, Query UNTERMINATED." The manual says this means: "The computer attempts to read a query response from the counter after having issued an incomplete query command. "The computer attempts to read a query response from the counter after having issued an incomplete query command." - which is not real helpful.
This is what I send to the counter:
// setup - no complaints
A53230A = new Ag532xx("TCPIP0::" + ipAddress + "::inst0::INSTR");
A53230A.SCPI.OPC.QueryTimeout = 60000;
// take a measurement
double freqmeas = null;
A53230A.SCPI.MEASure.SCALar.VOLTage.FREQuency.PRF.QueryAsciiReal(null, 1, "@3", out freqmeas);
The above command is actually in a try/except block and the exception error mentioned above is what I get. As near as I can tell (examples are sparse), the measure query is all I need. Since the inner workings are hidden, I don't know what the incomplete command would be.