The commands in the previous section only set up DetCom for the next exposure. Except for filter motion (if applicable), which begins immediately, nothing else happens to the instrument until a go is issued in the director window. Go takes an optional argument giving the number of iterations.
During the exposure phase of a go, it is possible to type stop in the director shell window. This is a special command which is processed immediately, as an interrupt to the current operation. (Other commands, such as another go will be queued up and processed after the current go has completed.)
As soon as the stop command is issued, the current integration will be ended (early) and the readout will begin. This is useful if clouds move in and the observer wishes to end an observation early, or if an incorrect exposure time was entered. It is not currently possible to modify the exposure time requested once an exposure has been started.
The break command is another special command, processed as an interrupt. For single exposures, it has no effect, but if multiple exposures are in progress, it causes the full current integration to complete but the subsequent one will not begin.
This is the third special interrupt command, and should be used with extreme caution. It expresses the users desire to stop whatever is happening immediately (which is not always possible). Note that this could include aborting the saving of a previous exposure, which may still be in progress.
If a readout is in progress, the abort command is currently disabled because in many cases the DSP has been left in an unpredictable state if aborted at that time.