Here are the answers to some questions about our new waveform stop master
which asked by someone. It certainly helps to make a real stop MASTER.
I thank you for your questions and suggestions. Again, I would like to
ask you to harass me with more questions. Dumb questions are welcome. I
was not able to program any chip later last week because our ACTEL
programmer had been moved and not yet been re-installed.
Q: Did the MASTER take computer busy into account?
A: Most scintillator triggers have been taken the computer busy signals
into account inside their circuits except the Caltech Slow Monopole
trigger. The waveform master will take the computer busy for the Caltech
Slow Monopole trigger. If the computer busy showed up before any slow
monopole trigger happened, it would freeze the slow monopole trigger
signals (not accept any slow monopole triggers). However, if any slow
monopole trigger happened before the computer busy signal, the master
would ignore any busy signals and finish its 1ms event cycle.
Q: What happens if two slow monopole triggers are from the same face?
A: The master will ignore any further slow monopole triggers from the
same face because they are not the coincidence events which we want.
Q: What is the decision for the inter-SM events?
A: The master is based on each SM. For the inter-SM events we should
check information and decide how to read out because 1ms delay has given
enough time to record all the events inside. For both FMT and CSPAM events,
two SM's waveforms will be stopped at the same time after 1ms delay. For
the ERP trigger, two SM's waveforms will be stopped separately if there
are two triggers happened for two SM's. Hence, for those who analyze the
data, it's a little bit more work. But the data are there!
Q: What if we decide change 1ms delay to some shorter time because the
trigger rates are too high?
A: In my last mail, I said that I was going to use a 14-bit
external switches. I have decided not to use that, but use
software instead. The master will be initialized at the beginning
of the RUN and the delay information will be written through CAMAC
bus. This time 16 bits all are under control.
Q: Who is going to clear the waveform digitizer?
A: The master has a inside register which registers all the triggers. By
checking that register in the readout, the last one will clear the system.
For example, if an event has both CSPAM and ERP triggers, the ERP will
check other bits before it clears the waveform. In this case, it will not
clear the waveforms because CSPAM triggered also. When the CSPAM finish
readout, it will check all the triggers and decide whether to clear or not.
Q: If a monopole trigger just happened before 1ms delay cycle, what does
the MASTER do?
A: There are two solutions to this question. The first is the same
as the current WFD setup. That is that the stop signal will be
delayed by another sufficiently long time in order to take care of
that monopole passing through our detector. In the new WFD system,
that means we have to wait another 1ms to obtain that goal. The
second answer is that we will forget any further delay and stop
the WFD's by only delay 1ms after the first trigger no matter when
the slow monopole trigger happens within that delay time. The
second answer sounds a little bit silly because we throw the event
away after we know that it is a trigger. However, I think the real
issue here is how long the delay can be so that the system can
handle. We already sacrifice 1ms to wait for the coincidence
signal coming out. Should we delay for another 1ms under the
condition that the slow monopole triggers? At this moment, the
MASTER will just go ahead without any further delay. But I think
people should think about it. I personally intend to make another
delay. Let me stress here that the further delay for slow monopole
doesn't happen all the time. For example, most of the slow
monopole triggers have only the Caltech slow monopole trigger
itself. Therefore, the stop signal will be only delayed by 1ms.
Some slow monopole triggers caused by muon events happened right
after the other muon triggers (about 5us late), therefore, the
extra delay is only several microseconds. Clearly the extra 1ms
delay only happens for a very small number of events.
Ciao,
--Rongzhi