ADLINK LPCI-7230 - Manual (Page 54)

46 Operation Theory
4.3 Change of State Detection
What is COS?
The COS (Change of State) occurs when the input state (logic
level) is changed from low to high or from high to low. The COS
detection circuit is used to detect the edge of level change. In the
PCI-7233 card, the COS detection circuit is applied to all 32 chan-
nels input channels. If any channel is changed, the COS detection
circuit generates an interrupt request signal.
Structure of COS detection and Dual Interrupt System
The dual interrupt system is used in PCI-7233. Dual interrupt
occurs when the hardware can generate two interrupt request sig-
nals at the same time and the software can service these two
requests with ISR. Note that dual interrupt does not mean the card
occupies two IRQ levels. The two interrupt request signals (INT1
and INT2) come from COS detection output signal #1 and #2. The
INT1 is inserted when any channel from 0 to 15 is changed. The
INT2 is inserted when any channel between 16 to 31 is changed.
The interrupt system is illustrated below.