SIS Documentation
SIS3820
VME Scaler
Page 24 of 79
The generation of the status flags, the IRQ flags and the actual IRQ is illustrated with the
schematic below:
Note:
Source 0 is shown as edge sensitive and source 1 as level sensitive input in the drawing
above. Which interrupt sources are edge and level sensitive may vary from firmware
implementation to firmware implementation.
7.4.1 Interrupt sources
A short explanation of the implemented interrupt sources is given in the following
subsections.
7.4.1.1 LNE/clock shadow (IRQ source 0; edge sensitive)
In multiscaler or multi channel scaler (MCS) mode interrupt source 0 is associated to the LNE
(load next event) signal. The interrupt is issued whenever a LNE signal triggers scaler value
transfer to memory. The interrupt will be induced by the rundown of the preset value if LNE
prescaling is active.
In scaler mode the LNE interrupt is driven by the clock shadow signal .
7.4.1.2 FIFO threshold (IRQ source 1; level sensitive)
The FIFO threshold IRQ source can be used for efficient readout in FIFO emulation mode.
The interrupt will be triggered as soon as the number of data words in memory will reach the
(non 0) value of the FIFO threshold register
AND
AND
AND
Enable 0
OR
Status IRQ
Source 0
Status IRQ
Source 1
Status IRQ
Source 7
Clear
Source 0
Enable 1
Enable 7
Source 1
Clear
Source 7
Status FLAG
Source 0
Status FLAG
Source 1
Status FLAG
Source 7
AND
Clear
IRQ (ROAK case)
internal
VME_IRQ
AND
IRQ_Update
O
R
MUX
VME IRQ
IRQ ACK cycle
VME IRQ enable
IRQ (RORA case)