Rockwell Automation 1746-HSCE,D17466.5 High-Speed Counter Module - Manual (Page 41)

Publication 1746-UM006B-EN-P - August 2005
Module Operation 2-23
Sequencer Mode Operation
A step is reached on the next count after the Accumulated Count
matches the Step Preset value. When a step is reached, the Step
Output value for that step is applied to the Physical and Soft Outputs.
When the sequencer is first enabled (or reset), the Initial Output
pattern (M0:e.3/8-15) is applied to the Physical and Soft Outputs. The
module then proceeds through each step in the sequence in
ascending order (1-24), as defined in the Valid Steps field (M0:e.2 to
M0:e.3/0-7).
After the sequencer has reached the last Valid Step, it wraps around to
the first available Step Preset (for example Step 1 Preset), making it
the next step (Next Sequencer Step, I:e.5/8-15). The pulse counter
must count one pulse beyond the Step Preset (for example Step 1
Preset) before the first Valid Step (for example Step 1) is reached.
For example, if Step 2 Preset (M0:e.18) contains a value of 99, the step
is reached one count after the Accumulated Count equals 99. If the
pulse counter is incrementing, the step is reached when the
Accumulated Count equals 100. If the pulse counter decrements, the
step is reached when the Accumulated Count equals 98.
The order of the Valid Steps is from low to high, as defined in the
Valid Steps field. If steps 1 and 3 are valid (enabled), step 1 will be
reached before step 3 regardless of the pulse counter value. Step 3
will be reached only after the following conditions are satisfied:
•
Step 1 has been reached.
•
The Accumulated Count is one step past the Step 3 Preset Value.
When step 3 is reached, the Step 3 Output pattern (M0:e.5/0-7) is
applied to the Physical and Soft Outputs. The Step 3 Output pattern
(M0:e.5/0-7) will be valid until the next Valid Step (step 1) is reached.
Unlike the Range and Rate Modes, the sequencer will not fall back to
a previous step just because the pulse counter again reaches one
count beyond the associated Step Preset. The sequencer is only
looking for the Next Sequencer Step (I:e.5/8-15) in the sequence. The
Next Sequencer Step Preset is located at I:e.7.
An example of sequencer operation with a ring counter is shown on
page 2-24. Here, the sequencer steps through 5 output patterns. This
example demonstrates that the sequence can be defined over several
counter rollovers. It also assumes that the Maximum Count Value is set
to 32,000.