SIS Documentation
SIS3820
VME Scaler
Page 10 of 79
4.2 Modes of operation
4.2.1 Scaler/Counter
In standard counter/scaler mode data can be read on the fly with an accuracy to the least
significant bit. No counts are lost in read on the fly mode.
4.2.2 Latching Scaler
In latching scaler mode scaler values are copied to a shadow register set upon a front panel
signal LNE or a VME command. Broadcast functionality is implemented for the later to allow
for minimum time difference over a set of several SIS3820s without front panel cabling.
4.2.3 Preset Scaler
The SIS3820 can be operated as preset scaler. An arbitrary channel or a combination of
channels can be selected as the condition for the termination of the counting process. The
selection of the channel(s) is done via the preset enable mask register . The first selected
channel that reaches its preset value will terminate the counting process. The actual preset
values are defined though the preset value register set. The internal 25 MHz pulse generator
(or a prescaled derived output) can be used as time base for measurements if its enabled for
channel 1 with this channel being enabled in the preset enable mask and the desired prescale
factor stored into the channel 1 preset value register. The terminating channel can be
identified by the actual scaler data or the preset hit mask register if more than one preset
channel is enabled.
4.2.4 Multi channel Scaler (MCS)
MCS mode allows for the buffered readout of variable or fixed lengths counting time
intervals. The interval length can be defined by an internal timer as well as by an external
signal, which can be prescaled also. The minimum buffer memory size of 64 MB takes the
realtime burden away from the VME master even at very short time intervals (dwell times).
Two factors facilitate short dwell time applications. The first is high speed VME readout of
data from SDRAM in MBLT64 and 2eVME. The second is data compression with a
reduction in counter depth to 16 or 8-bit. Data compression is also a good way to save VME
bandwidth in lower count rate applications (with V/F converters e.g.) at longer dwell times.
4.2.5 Histogramming Scaler(3820 01 02 and higher design)
Histogramming scaler mode (MCS mode with add enabled) allows to acquire and add MCS
data of several repeated scans in SDRAM without CPU interaction. The user has to make
sure, that the reset to the first bin and the number of bins are issued with the accuracy that is
required by the application. I.e. no number of bin/reset checking mechanism is implemented
(unlike in the SIS3100-HISCAL DSP based design).