Rockwell Automation 1746-HSCE2 Multi-Channel High Speed Counter Module - Manual (Page 66)

Publication 1746-UM002B-EN-P - August 2004
4-16 Configuration and Programming
always included with this block, and its value must fall between the
minimum/maximum count values.
The data is in the two-word integer format as described in Integer
Format on page 4-3.
Counter Type
The meanings of the minimum and maximum counter values are
dependent on the counter type.
Ring Counter
As a ring counter, the counter counts between the minimum and
maximum values. When counting up, if the maximum value is
reached, the counter rolls over to the minimum value. When counting
down, if the minimum value is reached, the counter rolls over to the
maximum value.
Linear Counter
As a linear counter, the counter counts between the minimum and the
maximum value. If the maximum value would be exceeded when the
counter is counting up, the counter stops counting and an overflow
bit is set in the status field of the counter. If, while counting down, the
counter reaches a value that would be less than the minimum value,
an underflow bit is set in the status field of the counter.
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.
If the linear counter is in an overflow/underflow state, the rate value
continues to update.
Minimum/Maximum Rate
Value Block Figure 4.7 shows the format of the Minimum/Maximum Rate Value
programming block. This block programs the minimum and maximum
rate values of the selected counter. All counters can be running when
this block is sent to the module.