SIS Documentation
SIS3820
VME Scaler
Page 66 of 79
15.5 Multiscaling (MCS)
Multi channel or multiscaling is a method to decouple the realtime behavior of fast counting
processes from the VME readout process. Data are buffered in an onboard memory and
readout at a later point in time in an asynchronous fashion. The SIS3820 uses standard 168-
pin SDRAM memory strips as buffer, the default size is 64 MBytes. The memory can be used
in:
•
SDRAM mode
•
FIFO mode
While SDRAM mode fits applications with a known number of acquisition cycles that will fit
into the SDRAM strip completely, FIFO mode allows for the sustained acquisition of
measurements of an arbitrary number of readout cycles under the assumption, that the VME
master is capable of digesting the generated data rate. The time slices (or load next
event=LNE cycles) can be defined by following processes:
•
VME LNE
•
external LNE signal
•
internal 10 MHz pulse generator
•
channel N as preset scaler
The later three can be routed through a prescaler.
15.5.1 Minimum dwell time
Find below a table with minimum dwell times for a number of configurations.
Number of channels Channel depth (bits) Dwell time in ns
32 32
960
16 32
500
8 32
340
32 16
660
16 16
340
8 16
260
32 8
500
16 8
260
8 8
220
Please note that a depth of 8 bits (i.e. 0-255 counts) is by far sufficient to hold all counts that
can occur at the maximum count rate and minimum dwell time. The minimum dwell time for
a given configuration can be measured on the CIP output (with output mode 1 and 2).
