VTI Instruments Corp.
24
EX1200-1538: Counter/Timer Operation
Ground
Level
Threshold Level
Hysteresis Band
Digital
Output
Pattern
F
IGURE
3-6:
C
ORRECT
T
HRESHOLD AND
H
YSTERESIS
U
SE
Polarity Conversion
Polarity selection allows for the digital signal to be inverted prior to being sent to the electronic
counter. By default, the signal is passed as an active High. When Inverted is selected, the signal is
sent as an active Low.
F
UNCTIONS
Totalizing
The
Totalize
function counts the total number of rising and falling edge transitions from an input
signal. Counting begins as soon as the card is
Armed
and continues until its operation is
Aborted
.
Any pulse with a width greater than 20 ns can be counted.
Input Logic Pattern
Count Value
1
2
3 4
5
6
7
(2
32
-1)
0
F
IGURE
3-7:
T
OTALIZE
F
UNCTION
Typically, counting begins from zero (0) and can continue up to 4,294,967,295 (2
32
-1) counts. If,
however, it is necessary to begin counting at some positive number other than 0, the
Preset Count
parameter can be used. Should the EX1200-1538 exceed the maximum count number, the user can
use one of three overflow modes for controlling how the data is managed:
STOP
,
PRESET
, and
WRAPAROUND
.
STOP
mode: the instrument stops counting once it “rolls over” (i.e. exceeds the maximum
count number) and returns an invalid value (NaN) as a result.
PRESET
mode: the instrument counter rolls over and begins counting again from the defined
Preset Count
parameter.
WRAPAROUND
mode: the instruments counter rolls over and begins counting again from
zero.
