76 34980A User’s Guide
2 Features and Functions
Using Alarms With the Digital Modules
You can configure the instrument to generate an alarm when a specific
bit pattern or bit pattern change is detected on a digital input channel
or when a specific count is reached on a totalizer channel (34950A and
34952A). These channels do not have to be part of the scan list to
generate an alarm. Alarms are evaluated continuously as soon as you
enable them.
• The channel numbering scheme for the digital input and totalizer
channels is shown below (s represents the slot number).
• Pattern comparisons always start on the lowest- numbered channel in
the bank and extend to all channels involved in the channel width.
• Alarms are evaluated continuously on the digital modules, but alarm
data is stored in reading memory only during a scan.
• Each time you start a new scan, the instrument clears all readings
(including alarm data) stored in reading memory from the previous
scan. However, alarm data stored in the alarm queue from the digital
modules is not cleared. Therefore, although the contents of reading
memory are always from the most recent scan, the alarm queue may
contain data that occurred during previous scans or while the
instrument was not scanning.
Front Panel Operation:
• To configure an alarm on a digital input channel, choose from the
following items and then set the desired patterns for the compare data
and mask. Set each bit to “0” or “1”.
Alarm > COMPARE DATA > COMPARE MASK
• You can either specify that an alarm will occur when certain bits
change or when a specific pattern is read:
Alarm > COMPARE FOR > EQUAL|NOT-EQ
• To configure an alarm on a specific totalizer count, select:
Alarm > TOTALIZER LIMIT
Digital Input Channel Numbering Totalizer Channel Numbering
34950A s101 through s104
s201 through s204
s301, s302
34952A s001 through s004 s005
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