Rockwell Automation 1734-VHSC24 Very High-Speed Counter Modules User Manual - Manual (Page 40)

Publication 1734-UM003B-EN-P - August 2000
3-10 Very High-Speed Counter Module Input and Output Data
Rollover (Configuration Word 10)
This long word sets the number of counts the counter accumulates
before rolling over. For example, a value of 1000 produces a count
sequence of: 998, 999, 0, 1, 2
… while incrementing or 2, 1, 0, 999,
998
… while decrementing. Rollover is a 32-bit number with a useable
range of 1
≤ value ≤ 0x01000000 (16,777,216). In PWM [3]
configuration, this value should be zero; in count [0], x1 encoder [1],
x2 encoder [2] and x4 encoder [4] configurations, it should be
specified to some non-zero value; and in period/rate [5], continuous/
rate [6] and rate measurement [7] configurations is a ‘don’t care’.
Preset (Configuration Word 11)
This long word sets the preset value the counter is loaded with, when
a Counter Preset, CP, command is issued. Preset is a 32-bit number
with a range of 0
≤ value ≤ 0x00FFFFFF (16,777,215).
Counter ON and OFF Windows (Configuration Words 12 to 19)
These long words program the four compare window's ON and OFF
values. The first compare window for each counter is used in PWM [3]
configuration and, when PWM is programmed for a channel, the
associated compare window should remain at 0. The range of each
entry is 0
≤ value ≤ 0x00FFFFFF (16,777,215). When a tie is connected
to a compare window, that window must be specified (ON value
≠
OFF value
≠ 0). These windows are always interpreted as counts,
regardless of the configuration setting and may be computed as
follows for frequency modes 5, 6, and 7:
Period/Rate (5) and Continuous Rate
counts = ( scalar x 2.5E6 ) / desired_frequency
Rate Measurement
counts = time_base [sec] x gate_interval x desired_frequency