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User's Manual (MUT)
Mod. DT5740 32 Channel 12bit - 65MS/s Digitizer
04/05/2016
12
NPO:
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00100/09:5740x.MUTx/12
DT5740_REV12.DOC
50
22
3.3
Acquisition Modes
3.3.1
Acquisition Run/Stop
The acquisition can be started and stopped in different ways, according to bits[1:0] setting of
Acquisition Control register (address 0x8100) and bit[2] of the same register:
SW CONTROLLED (bits[1:0] = 00): Start and Stop take place by software command. Bit[2] = 0
means stopped, while bit[2] = 1 means running.
GPI CONTROLLED MODE (bits[1:0] = 01): If the acquisition is armed (i.e. bit[2] = 1), then Run
starts when GPI is asserted and stops when GPI returns inactive. If bit[2] = 0, the acquisition
is always off.
FIRST TRIGGER CONTROLLED (bits[1:0] = 10): bit[2] = 1 arms the acquisition and the Start is
issued on the first trigger pulse (rising edge) on the TRG-IN connector. This pulse is not used
as a trigger; actual triggers start from the second pulse on TRG-IN. The Stop acquisition must
be SW controlled (i.e. reset of bit[2]).
3.3.2
Acquisition Triggering: Samples and Events
When the acquisition is running, a trigger signal allows to:
store a 31-bit counter value of the Trigger Time Tag (TTT).
The counter (representing a time reference), like so the Trigger Logic Unit (see § 3.2)
operates at a frequency of 125 MHz (i.e. 8 ns, that is to say ½ ADC clock cycles). Due to the
way the acquired data are written into the board internal memory (i.e in 4-sample bunches),
the TTT counter is read every 2 trigger logic clock cycles, which means the trigger time
stamp resolution results in 16 ns (i.e. 62.5 MHz). Basing on that, the LSB of the TTT is always
“0”;
increment the EVENT COUNTER;
fill the active buffer with the pre/post-trigger samples, whose number is programmable
(record length), freezing then the buffer for readout purposes, while acquisition continues
on another buffer.
An event is therefore composed by the trigger time tag, pre- and post-trigger samples and the
event counter.
Overlap between “acquisition windows” may occur (a new trigger occurs while the board is still
storing the samples related to the previous trigger); this overlap can be either rejected or
accepted (programmable via software).
If the board is programmed to accept the overlapped triggers, as the “overlapping” trigger
arrives, the current active buffer is filled up, then the samples storage continues on the
subsequent one.In this case events will not have all the same size (see Fig. 3.3 below).
