24
[(maximum time range s 15) - difference], where difference is from
the table below.
Resolution
Edge Mode
Difference
0.5 nsec
leading edge only
1023
both edges
511
1.0 nsec
leading edge only
2047
both edges
1023
2.0 nsec
leading edge only
4095
both edges
2047
4.0 nsec
leading
8191
both edges
4095
For 2 nsec resolution and both edge mode, the difference is 2047. For an
offset of 512 nsec (a multiple of 8 nsec), the maximum time range value
should be 1528 nsec (also a multiple of 8 nsec). There are 512 possible
data values, from 0 to 1022 nsec. A raw data value of 512 through 513.5
nsec will be readout as zero, the raw data value of 1534 through 1535.5
nsec will be read out as 1022 nsec.
NOTE:
Any data which occurs between the lower bound of the window
and the common STOP will still be recorded, and will occupy storage
space in the MTD133 chip. If a time window is used, it is recommended to
set the maximum number of hits to 16, and that the offset value be small.
Dead Time
The 3377 is a pipelined TDC, and the pipeline is stopped during the
transfer of the hit data from the chips to the FIFO event buffer on the
board. The time to buffer the data is typically 1.8
µ
s + 100 nsec per hit.
During this time the front panel BUSY output is asserted and the module
responds with Q=1 to an F27, A1 command. Any inputs received at the
front panel will be ignored during this period. Only when buffering of the
data is complete and the BUSY is turned off is the module ready to
receive data at the front panel signal inputs.
The trigger system must wait for the pipeline to refill before sending a new
common stop signal. This refill time should be equal to the maximum time
range selected in register 2. It is the responsibility of the trigger system to
provide this delay. If a common stop is received before the pipeline has
completely refilled (before the maximum time has passed), then valid hits
that occurred within the maximum time range, but during the dead time,
will not be recorded. If the 3377 is not set to buffer the data then busy will
remain on until the data is read out of the unit.
Front Panel Clear Input
This input is used to clear an event in progress. The CLEAR is effective
ONLY between the COMMON STOP and the end of MPI “Measured Pulse
Interval (MPI)”. If MPI is set to 0, the CLEAR is ignored. To be reliable, the
CLEAR must arrive at least 100 nsec AFTER the leading edge of the
COMMON STOP, and at least 100 nsec BEFORE the end of MPI (COM-
MON STOP time plus the MPI setting). The CLEAR signal is synchronized
internally with the 100 nsec system clock, and its behavior exhibits 100
nsec of jitter due to the random phase of this clock with respect to the
external input signals.