ADLINK PXI-7901 - Manual (Page 18)

12 • Operation Theorem
4.2 Operation Mode
The ADLINK PXI Switch Module provides two relay operation modes to
accommodate different application requirements.
Direct-update
The Switch Module updates the relay pattern immediately upon receiving a
software command. This mode provides a straightforward control over switch
module with minimal hardware intervention. If relay contact bouncing is of a
concern, users would need to insert software delay.
ADLINK recommends the debounce time to be at least 8ms on PXI-7901.
Auto-scan
The ADLINK PXI switch module features onboard memory to store user
specified scanlist of up to 1024-entry. In each scanlist entry, users can specify
relay pattern, pattern advancing delay time and criterion.
The switch module can set status bit or generate local interrupt to inform user’s
program whether the pattern has been debounced and advanced to the next
scanlist entry. Users can also specify one-time or cyclic scanning of scanlist
entries.
This operating mode supports trigger signals for instrument handshaking. For
more information on handshaking signals, please refer to section 4.3
.
4.3 Handshaking
In the Auto-scan mode, ADLINK PXI switch module accepts Trigger In and
generates Scanner Advanced signal to synchronize relay switching and
measurements with PXI instruments or external measurement devices.
Trigger In
The Trigger In signal from PXI instruments or external measurement devices
instruct the ADLINK PXI switch module to update the relay pattern according to
the one specified in the scanlist entry.
Users may specify wait-for-trigger instruction in a scanlist entry, to have the
switch module wait for the Trigger In before relay pattern is updated. The
polarity of Trigger In can be set to either rising-edge or falling-edge active.
For more information on scanlist configuration, please refer to the software
programming users’ guide.