Rockwell Automation 1746-HSCE2 Multi-Channel High Speed Counter Module - Manual (Page 29)

Publication 1746-UM002B-EN-P - August 2004
Module Operation 2-9
Counter Types Each counter can be programmed to operate as a linear or ring
counter. Both types are described below.
Linear Counter
The figure below demonstrates linear counter operation. In linear
operation, the count value must remain within the programmed
minimum/maximum values. If the count value goes above or below
these values, the counter stops counting, and an overflow/underflow
bit is set. In the overflow or underflow condition, the rate value
continues to be updated and valid.
The number of pulses accumulated in an overflow/underflow state
are ignored. The counter begins counting again when pulses are
applied in the proper direction. For example, if you exceed the
maximum by 1,000 counts, you do not need to apply 1,000 counts in
the opposite direction before the counter begins counting down. The
first pulse in the opposite direction decrements the counter.
Figure 2.5 Linear Counter Diagram
Count Up
Count Down
Counter Value
Maximum Value
Overflow
Minimum Value
Underflow
0