How do you prevent the counter from hanging up the GPIB bus when no signal is applied?

When the counter is programmed to make a measurement, it waits until a signal is applied and then makes the measurement. When no signal is applied, and if using the MEASure? or READ? command, the counter will hang up the GPIB bus until a signal is applied and it makes the measurement. To prevent this from happening, set the GPIB timeout value to a sufficient value to complete the measurement. Whenever the timeout value is reached, the GPIB bus will then timeout.

This method does generate an error and, since the counter is still waiting to make the measurement, it will be locked up and no commands can be executed by the counter, until unlocked. To unlock the counter, apply a signal to it to make the measurement. If not possible, then execute a GPIB Device Clear, and then read the counter's error register using the SYSTem:ERRor? command to clear the register.

Another way to prevent this from happening is to use the CONFigure, INITiate, and FETCh? commands to configure the counter and make the measurement. Use the CONFigure and associated commands to setup the counter and then the INITiate command to start the measurement. In this case, the GPIB bus will not hang. The counter will, however, hang the bus if sending the FETCh? command when no measurement has been made.